COMMIT
 (33 rows)
 
+-- MERGE support
+BEGIN;
+MERGE INTO replication_example t
+   USING (SELECT i as id, i as data, i as num FROM generate_series(-20, 5) i) s
+   ON t.id = s.id
+   WHEN MATCHED AND t.id < 0 THEN
+       UPDATE SET somenum = somenum + 1
+   WHEN MATCHED AND t.id >= 0 THEN
+       DELETE
+   WHEN NOT MATCHED THEN
+       INSERT VALUES (s.*);
+COMMIT;
+/* display results */
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
+                                                                       data                                                                       
+--------------------------------------------------------------------------------------------------------------------------------------------------
+ BEGIN
+ table public.replication_example: INSERT: id[integer]:-20 somedata[integer]:-20 somenum[integer]:-20 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: INSERT: id[integer]:-19 somedata[integer]:-19 somenum[integer]:-19 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: INSERT: id[integer]:-18 somedata[integer]:-18 somenum[integer]:-18 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: INSERT: id[integer]:-17 somedata[integer]:-17 somenum[integer]:-17 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: INSERT: id[integer]:-16 somedata[integer]:-16 somenum[integer]:-16 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-15 somedata[integer]:-15 somenum[integer]:-14 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-14 somedata[integer]:-14 somenum[integer]:-13 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-13 somedata[integer]:-13 somenum[integer]:-12 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-12 somedata[integer]:-12 somenum[integer]:-11 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-11 somedata[integer]:-11 somenum[integer]:-10 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-10 somedata[integer]:-10 somenum[integer]:-9 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-9 somedata[integer]:-9 somenum[integer]:-8 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-8 somedata[integer]:-8 somenum[integer]:-7 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-7 somedata[integer]:-7 somenum[integer]:-6 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-6 somedata[integer]:-6 somenum[integer]:-5 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-5 somedata[integer]:-5 somenum[integer]:-4 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-4 somedata[integer]:-4 somenum[integer]:-3 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-3 somedata[integer]:-3 somenum[integer]:-2 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-2 somedata[integer]:-2 somenum[integer]:-1 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: UPDATE: id[integer]:-1 somedata[integer]:-1 somenum[integer]:0 zaphod1[integer]:null zaphod2[integer]:null
+ table public.replication_example: DELETE: id[integer]:0
+ table public.replication_example: DELETE: id[integer]:1
+ table public.replication_example: DELETE: id[integer]:2
+ table public.replication_example: DELETE: id[integer]:3
+ table public.replication_example: DELETE: id[integer]:4
+ table public.replication_example: DELETE: id[integer]:5
+ COMMIT
+(28 rows)
+
 CREATE TABLE tr_unique(id2 serial unique NOT NULL, data int);
 INSERT INTO tr_unique(data) VALUES(10);
 ALTER TABLE tr_unique RENAME TO tr_pkey;
 
 /* display results */
 SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
 
+-- MERGE support
+BEGIN;
+MERGE INTO replication_example t
+   USING (SELECT i as id, i as data, i as num FROM generate_series(-20, 5) i) s
+   ON t.id = s.id
+   WHEN MATCHED AND t.id < 0 THEN
+       UPDATE SET somenum = somenum + 1
+   WHEN MATCHED AND t.id >= 0 THEN
+       DELETE
+   WHEN NOT MATCHED THEN
+       INSERT VALUES (s.*);
+COMMIT;
+
+/* display results */
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
+
 CREATE TABLE tr_unique(id2 serial unique NOT NULL, data int);
 INSERT INTO tr_unique(data) VALUES(10);
 ALTER TABLE tr_unique RENAME TO tr_pkey;
 
        <structname>PGresult</structname>. This function can only be used following
        the execution of a <command>SELECT</command>, <command>CREATE TABLE AS</command>,
        <command>INSERT</command>, <command>UPDATE</command>, <command>DELETE</command>,
-       <command>MOVE</command>, <command>FETCH</command>, or <command>COPY</command> statement,
-       or an <command>EXECUTE</command> of a prepared query that contains an
-       <command>INSERT</command>, <command>UPDATE</command>, or <command>DELETE</command> statement.
+       <command>MERGE</command>, <command>MOVE</command>, <command>FETCH</command>,
+       or <command>COPY</command> statement, or an <command>EXECUTE</command> of a
+       prepared query that contains an <command>INSERT</command>,
+       <command>UPDATE</command>, <command>DELETE</command>
+       or <command>MERGE</command> statement.
        If the command that generated the <structname>PGresult</structname> was anything
        else, <function>PQcmdTuples</function> returns an empty string. The caller
        should not free the return value directly. It will be freed when
 
     <literal>11</literal>, which no longer matches the criteria.
    </para>
 
+   <para>
+    The <command>MERGE</command> allows the user to specify various combinations
+    of <command>INSERT</command>, <command>UPDATE</command> or
+    <command>DELETE</command> subcommands. A <command>MERGE</command> command
+    with both <command>INSERT</command> and <command>UPDATE</command>
+    subcommands looks similar to <command>INSERT</command> with an
+    <literal>ON CONFLICT DO UPDATE</literal> clause but does not guarantee
+    that either <command>INSERT</command> and <command>UPDATE</command> will occur.
+
+    If MERGE attempts an UPDATE or DELETE and the row is concurrently updated
+    but the join condition still passes for the current target and the current
+    source tuple, then MERGE will behave the same as the UPDATE or DELETE commands
+    and perform its action on the latest version of the row, using standard
+    EvalPlanQual. MERGE actions can be conditional, so conditions must be
+    re-evaluated on the latest row, starting from the first action.
+
+    On the other hand, if the row is concurrently updated or deleted so that
+    the join condition fails, then MERGE will execute a NOT MATCHED action, if it
+    exists and the AND WHEN qual evaluates to true.
+
+    If MERGE attempts an INSERT and a unique index is present and a duplicate
+    row is concurrently inserted then a uniqueness violation is raised. MERGE
+    does not attempt to avoid the ERROR by attempting an UPDATE.
+   </para>
+
    <para>
     Because Read Committed mode starts each command with a new snapshot
     that includes all transactions committed up to that instant,
 
         <para>
          The commands <command>UPDATE</command>,
-         <command>DELETE</command>, and <command>INSERT</command>
+         <command>DELETE</command>, <command>INSERT</command> and
+         <command>MERGE</command>
          acquire this lock mode on the target table (in addition to
          <literal>ACCESS SHARE</literal> locks on any other referenced
          tables).  In general, this lock mode will be acquired by any
 
 </programlisting>
      Another restriction on parameter symbols is that they only work in
      <command>SELECT</command>, <command>INSERT</command>, <command>UPDATE</command>, and
-     <command>DELETE</command> commands.  In other statement
+     <command>DELETE</command> and <command>MERGE</command> commands.  In other statement
      types (generically called utility statements), you must insert
      values textually even if they are just data values.
     </para>
           <listitem>
            <para>
             <command>UPDATE</command>, <command>INSERT</command>, and <command>DELETE</command>
+            and <command>MERGE</command>
             statements set <literal>FOUND</literal> true if at least one
             row is affected, false if no row is affected.
            </para>
 
 <!ENTITY load               SYSTEM "load.sgml">
 <!ENTITY lock               SYSTEM "lock.sgml">
 <!ENTITY move               SYSTEM "move.sgml">
+<!ENTITY merge              SYSTEM "merge.sgml">
 <!ENTITY notify             SYSTEM "notify.sgml">
 <!ENTITY prepare            SYSTEM "prepare.sgml">
 <!ENTITY prepareTransaction SYSTEM "prepare_transaction.sgml">
 
    exist, a <quote>default deny</quote> policy is assumed, so that no rows will
    be visible or updatable.
   </para>
+
+  <para>
+   No separate policy exists for <command>MERGE</command>. Instead policies
+   defined for <literal>SELECT</literal>, <literal>INSERT</literal>,
+   <literal>UPDATE</literal> and <literal>DELETE</literal> are applied
+   while executing MERGE, depending on the actions that are activated.
+  </para>
  </refsect1>
 
  <refsect1>
 
    is a partition, an error will occur if one of the input rows violates
    the partition constraint.
   </para>
+
+  <para>
+   You may also wish to consider using <command>MERGE</command>, since that
+   allows mixed <command>INSERT</command>, <command>UPDATE</command> and
+   <command>DELETE</command> within a single statement.
+   See <xref linkend="sql-merge"/>.
+  </para>
  </refsect1>
 
  <refsect1>
    Also, the case in
    which a column name list is omitted, but not all the columns are
    filled from the <literal>VALUES</literal> clause or <replaceable>query</replaceable>,
-   is disallowed by the standard.
+   is disallowed by the standard. If you prefer a more SQL Standard
+   conforming statement than <literal>ON CONFLICT</literal>, see
+   <xref linkend="sql-merge"/>.
   </para>
 
   <para>
 
    &listen;
    &load;
    &lock;
+   &merge;
    &move;
    ¬ify;
    &prepare;
 
     will be fired.
    </para>
 
+   <para>
+    No separate triggers are defined for <command>MERGE</command>. Instead,
+    statement-level or row-level <command>UPDATE</command>,
+    <command>DELETE</command> and <command>INSERT</command> triggers are fired
+    depending on what actions are specified in the <command>MERGE</command> query
+    and what actions are activated.
+   </para>
+
+   <para>
+    While running a <command>MERGE</command> command, statement-level
+    <literal>BEFORE</literal> and <literal>AFTER</literal> triggers are fired for
+    events specified in the actions of the <command>MERGE</command> command,
+    irrespective of whether the action is finally activated or not. This is same as
+    an <command>UPDATE</command> statement that updates no rows, yet
+    statement-level triggers are fired. The row-level triggers are fired only
+    when a row is actually updated, inserted or deleted. So it's perfectly legal
+    that while statement-level triggers are fired for certain type of action, no
+    row-level triggers are fired for the same kind of action.
+   </para>
+
    <para>
     Trigger functions invoked by per-statement triggers should always
     return <symbol>NULL</symbol>. Trigger functions invoked by per-row
 
               result == HeapTupleUpdated ||
               result == HeapTupleBeingUpdated);
        Assert(!(tp.t_data->t_infomask & HEAP_XMAX_INVALID));
+       hufd->result = result;
        hufd->ctid = tp.t_data->t_ctid;
        hufd->xmax = HeapTupleHeaderGetUpdateXid(tp.t_data);
        if (result == HeapTupleSelfUpdated)
 HTSU_Result
 heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
            CommandId cid, Snapshot crosscheck, bool wait,
-           HeapUpdateFailureData *hufd, LockTupleMode *lockmode)
+           HeapUpdateFailureData *hufd)
 {
    HTSU_Result result;
    TransactionId xid = GetCurrentTransactionId();
                infomask2_old_tuple,
                infomask_new_tuple,
                infomask2_new_tuple;
+   LockTupleMode   lockmode;
 
    Assert(ItemPointerIsValid(otid));
+   Assert(hufd != NULL);
 
    /*
     * Forbid this during a parallel operation, lest it allocate a combocid.
     */
    if (!bms_overlap(modified_attrs, key_attrs))
    {
-       *lockmode = LockTupleNoKeyExclusive;
+       lockmode = hufd->lockmode = LockTupleNoKeyExclusive;
        mxact_status = MultiXactStatusNoKeyUpdate;
        key_intact = true;
 
    }
    else
    {
-       *lockmode = LockTupleExclusive;
+       lockmode = hufd->lockmode = LockTupleExclusive;
        mxact_status = MultiXactStatusUpdate;
        key_intact = false;
    }
            int         remain;
 
            if (DoesMultiXactIdConflict((MultiXactId) xwait, infomask,
-                                       *lockmode))
+                                       lockmode))
            {
                LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
 
                /* acquire tuple lock, if necessary */
-               heap_acquire_tuplock(relation, &(oldtup.t_self), *lockmode,
+               heap_acquire_tuplock(relation, &(oldtup.t_self), lockmode,
                                     LockWaitBlock, &have_tuple_lock);
 
                /* wait for multixact */
             * lock.
             */
            LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
-           heap_acquire_tuplock(relation, &(oldtup.t_self), *lockmode,
+           heap_acquire_tuplock(relation, &(oldtup.t_self), lockmode,
                                 LockWaitBlock, &have_tuple_lock);
            XactLockTableWait(xwait, relation, &oldtup.t_self,
                              XLTW_Update);
               result == HeapTupleUpdated ||
               result == HeapTupleBeingUpdated);
        Assert(!(oldtup.t_data->t_infomask & HEAP_XMAX_INVALID));
+       hufd->result = result;
        hufd->ctid = oldtup.t_data->t_ctid;
        hufd->xmax = HeapTupleHeaderGetUpdateXid(oldtup.t_data);
        if (result == HeapTupleSelfUpdated)
            hufd->cmax = InvalidCommandId;
        UnlockReleaseBuffer(buffer);
        if (have_tuple_lock)
-           UnlockTupleTuplock(relation, &(oldtup.t_self), *lockmode);
+           UnlockTupleTuplock(relation, &(oldtup.t_self), lockmode);
        if (vmbuffer != InvalidBuffer)
            ReleaseBuffer(vmbuffer);
        bms_free(hot_attrs);
    compute_new_xmax_infomask(HeapTupleHeaderGetRawXmax(oldtup.t_data),
                              oldtup.t_data->t_infomask,
                              oldtup.t_data->t_infomask2,
-                             xid, *lockmode, true,
+                             xid, lockmode, true,
                              &xmax_old_tuple, &infomask_old_tuple,
                              &infomask2_old_tuple);
 
        compute_new_xmax_infomask(HeapTupleHeaderGetRawXmax(oldtup.t_data),
                                  oldtup.t_data->t_infomask,
                                  oldtup.t_data->t_infomask2,
-                                 xid, *lockmode, false,
+                                 xid, lockmode, false,
                                  &xmax_lock_old_tuple, &infomask_lock_old_tuple,
                                  &infomask2_lock_old_tuple);
 
     * Release the lmgr tuple lock, if we had it.
     */
    if (have_tuple_lock)
-       UnlockTupleTuplock(relation, &(oldtup.t_self), *lockmode);
+       UnlockTupleTuplock(relation, &(oldtup.t_self), lockmode);
 
    pgstat_count_heap_update(relation, use_hot_update);
 
 {
    HTSU_Result result;
    HeapUpdateFailureData hufd;
-   LockTupleMode lockmode;
 
    result = heap_update(relation, otid, tup,
                         GetCurrentCommandId(true), InvalidSnapshot,
                         true /* wait for commit */ ,
-                        &hufd, &lockmode);
+                        &hufd);
    switch (result)
    {
        case HeapTupleSelfUpdated:
        Assert(result == HeapTupleSelfUpdated || result == HeapTupleUpdated ||
               result == HeapTupleWouldBlock);
        Assert(!(tuple->t_data->t_infomask & HEAP_XMAX_INVALID));
+       hufd->result = result;
        hufd->ctid = tuple->t_data->t_ctid;
        hufd->xmax = HeapTupleHeaderGetUpdateXid(tuple->t_data);
        if (result == HeapTupleSelfUpdated)
 
 F311   Schema definition statement 03  CREATE VIEW YES 
 F311   Schema definition statement 04  CREATE VIEW: WITH CHECK OPTION  YES 
 F311   Schema definition statement 05  GRANT statement YES 
-F312   MERGE statement         NO  consider INSERT ... ON CONFLICT DO UPDATE
-F313   Enhanced MERGE statement            NO  
-F314   MERGE statement with DELETE branch          NO  
+F312   MERGE statement         YES also consider INSERT ... ON CONFLICT DO UPDATE
+F313   Enhanced MERGE statement            YES 
+F314   MERGE statement with DELETE branch          YES 
 F321   User authorization          YES 
 F341   Usage tables            NO  no ROUTINE_*_USAGE tables
 F361   Subprogram support          YES 
 
                case CMD_DELETE:
                    pname = operation = "Delete";
                    break;
+               case CMD_MERGE:
+                   pname = operation = "Merge";
+                   break;
                default:
                    pname = "???";
                    break;
            operation = "Delete";
            foperation = "Foreign Delete";
            break;
+       case CMD_MERGE:
+           operation = "Merge";
+           foperation = "Foreign Merge";
+           break;
        default:
            operation = "???";
            foperation = "Foreign ???";
                                 other_path, 0, es);
        }
    }
+   else if (node->operation == CMD_MERGE)
+   {
+       /* EXPLAIN ANALYZE display of actual outcome for each tuple proposed */
+       if (es->analyze && mtstate->ps.instrument)
+       {
+           double      total;
+           double      insert_path;
+           double      update_path;
+           double      delete_path;
+           double      skipped_path;
+
+           InstrEndLoop(mtstate->mt_plans[0]->instrument);
+
+           /* count the number of source rows */
+           total = mtstate->mt_plans[0]->instrument->ntuples;
+           insert_path = mtstate->ps.instrument->nfiltered1;
+           update_path = mtstate->ps.instrument->nfiltered2;
+           delete_path = mtstate->ps.instrument->nfiltered3;
+           skipped_path = total - insert_path - update_path - delete_path;
+
+           ExplainPropertyFloat("Tuples Inserted", NULL, insert_path, 0, es);
+           ExplainPropertyFloat("Tuples Updated", NULL, update_path, 0, es);
+           ExplainPropertyFloat("Tuples Deleted", NULL, delete_path, 0, es);
+           ExplainPropertyFloat("Tuples Skipped", NULL, skipped_path, 0, es);
+       }
+   }
 
    if (labeltargets)
        ExplainCloseGroup("Target Tables", "Target Tables", false, es);
 
        case CMD_INSERT:
        case CMD_UPDATE:
        case CMD_DELETE:
+       case CMD_MERGE:
            /* OK */
            break;
        default:
 
                   ResultRelInfo *relinfo,
                   ItemPointer tid,
                   LockTupleMode lockmode,
-                  TupleTableSlot **newSlot);
+                  TupleTableSlot **newSlot,
+                  HeapUpdateFailureData *hufdp);
 static bool TriggerEnabled(EState *estate, ResultRelInfo *relinfo,
               Trigger *trigger, TriggerEvent event,
               Bitmapset *modifiedCols,
 ExecBRDeleteTriggers(EState *estate, EPQState *epqstate,
                     ResultRelInfo *relinfo,
                     ItemPointer tupleid,
-                    HeapTuple fdw_trigtuple)
+                    HeapTuple fdw_trigtuple,
+                    HeapUpdateFailureData *hufdp)
 {
    TriggerDesc *trigdesc = relinfo->ri_TrigDesc;
    bool        result = true;
    if (fdw_trigtuple == NULL)
    {
        trigtuple = GetTupleForTrigger(estate, epqstate, relinfo, tupleid,
-                                      LockTupleExclusive, &newSlot);
+                                      LockTupleExclusive, &newSlot, hufdp);
        if (trigtuple == NULL)
            return false;
    }
                                           relinfo,
                                           tupleid,
                                           LockTupleExclusive,
+                                          NULL,
                                           NULL);
        else
            trigtuple = fdw_trigtuple;
                     ResultRelInfo *relinfo,
                     ItemPointer tupleid,
                     HeapTuple fdw_trigtuple,
-                    TupleTableSlot *slot)
+                    TupleTableSlot *slot,
+                    HeapUpdateFailureData *hufdp)
 {
    TriggerDesc *trigdesc = relinfo->ri_TrigDesc;
    HeapTuple   slottuple = ExecMaterializeSlot(slot);
    {
        /* get a copy of the on-disk tuple we are planning to update */
        trigtuple = GetTupleForTrigger(estate, epqstate, relinfo, tupleid,
-                                      lockmode, &newSlot);
+                                      lockmode, &newSlot, hufdp);
        if (trigtuple == NULL)
            return NULL;        /* cancel the update action */
    }
                                           relinfo,
                                           tupleid,
                                           LockTupleExclusive,
+                                          NULL,
                                           NULL);
        else
            trigtuple = fdw_trigtuple;
                   ResultRelInfo *relinfo,
                   ItemPointer tid,
                   LockTupleMode lockmode,
-                  TupleTableSlot **newSlot)
+                  TupleTableSlot **newSlot,
+                  HeapUpdateFailureData *hufdp)
 {
    Relation    relation = relinfo->ri_RelationDesc;
    HeapTupleData tuple;
                               estate->es_output_cid,
                               lockmode, LockWaitBlock,
                               false, &buffer, &hufd);
+
+       /* Let the caller know about failure reason, if any. */
+       if (hufdp)
+           *hufdp = hufd;
+
        switch (test)
        {
            case HeapTupleSelfUpdated:
                    /* it was updated, so look at the updated version */
                    TupleTableSlot *epqslot;
 
+                   /*
+                    * If we're running MERGE then we must install the
+                    * new tuple in the slot of the underlying join query and
+                    * not the result relation itself. If the join does not
+                    * yield any tuple, the caller will take the necessary
+                    * action.
+                    */
                    epqslot = EvalPlanQual(estate,
                                           epqstate,
                                           relation,
-                                          relinfo->ri_RangeTableIndex,
+                                          GetEPQRangeTableIndex(relinfo),
                                           lockmode,
                                           &hufd.ctid,
                                           hufd.xmax);
    bool        before_trig_done;   /* did we already queue BS triggers? */
    bool        after_trig_done;    /* did we already queue AS triggers? */
    AfterTriggerEventList after_trig_events;    /* if so, saved list pointer */
-   Tuplestorestate *old_tuplestore;    /* "old" transition table, if any */
-   Tuplestorestate *new_tuplestore;    /* "new" transition table, if any */
+   /* "old" transition table for UPDATE, if any */
+   Tuplestorestate *old_upd_tuplestore;
+   /* "new" transition table for UPDATE, if any */
+   Tuplestorestate *new_upd_tuplestore;
+   /* "old" transition table for DELETE, if any */
+   Tuplestorestate *old_del_tuplestore;
+   /* "new" transition table INSERT, if any */
+   Tuplestorestate *new_ins_tuplestore;
 };
 
 static AfterTriggersData afterTriggers;
    {
        if (LocTriggerData.tg_trigger->tgoldtable)
        {
-           LocTriggerData.tg_oldtable = evtshared->ats_table->old_tuplestore;
+           if (TRIGGER_FIRED_BY_UPDATE(evtshared->ats_event))
+               LocTriggerData.tg_oldtable = evtshared->ats_table->old_upd_tuplestore;
+           else
+               LocTriggerData.tg_oldtable = evtshared->ats_table->old_del_tuplestore;
            evtshared->ats_table->closed = true;
        }
 
        if (LocTriggerData.tg_trigger->tgnewtable)
        {
-           LocTriggerData.tg_newtable = evtshared->ats_table->new_tuplestore;
+           if (TRIGGER_FIRED_BY_INSERT(evtshared->ats_event))
+               LocTriggerData.tg_newtable = evtshared->ats_table->new_ins_tuplestore;
+           else
+               LocTriggerData.tg_newtable = evtshared->ats_table->new_upd_tuplestore;
            evtshared->ats_table->closed = true;
        }
    }
 MakeTransitionCaptureState(TriggerDesc *trigdesc, Oid relid, CmdType cmdType)
 {
    TransitionCaptureState *state;
-   bool        need_old,
-               need_new;
+   bool        need_old_upd,
+               need_new_upd,
+               need_old_del,
+               need_new_ins;
    AfterTriggersTableData *table;
    MemoryContext oldcxt;
    ResourceOwner saveResourceOwner;
    switch (cmdType)
    {
        case CMD_INSERT:
-           need_old = false;
-           need_new = trigdesc->trig_insert_new_table;
+           need_old_upd = need_old_del = need_new_upd = false;
+           need_new_ins = trigdesc->trig_insert_new_table;
            break;
        case CMD_UPDATE:
-           need_old = trigdesc->trig_update_old_table;
-           need_new = trigdesc->trig_update_new_table;
+           need_old_upd = trigdesc->trig_update_old_table;
+           need_new_upd = trigdesc->trig_update_new_table;
+           need_old_del = need_new_ins = false;
            break;
        case CMD_DELETE:
-           need_old = trigdesc->trig_delete_old_table;
-           need_new = false;
+           need_old_del = trigdesc->trig_delete_old_table;
+           need_old_upd = need_new_upd = need_new_ins = false;
+           break;
+       case CMD_MERGE:
+           need_old_upd = trigdesc->trig_update_old_table;
+           need_new_upd = trigdesc->trig_update_new_table;
+           need_old_del = trigdesc->trig_delete_old_table;
+           need_new_ins = trigdesc->trig_insert_new_table;
            break;
        default:
            elog(ERROR, "unexpected CmdType: %d", (int) cmdType);
-           need_old = need_new = false;    /* keep compiler quiet */
+           /* keep compiler quiet */
+           need_old_upd = need_new_upd = need_old_del = need_new_ins = false;
            break;
    }
-   if (!need_old && !need_new)
+   if (!need_old_upd && !need_new_upd && !need_new_ins && !need_old_del)
        return NULL;
 
    /* Check state, like AfterTriggerSaveEvent. */
    saveResourceOwner = CurrentResourceOwner;
    CurrentResourceOwner = CurTransactionResourceOwner;
 
-   if (need_old && table->old_tuplestore == NULL)
-       table->old_tuplestore = tuplestore_begin_heap(false, false, work_mem);
-   if (need_new && table->new_tuplestore == NULL)
-       table->new_tuplestore = tuplestore_begin_heap(false, false, work_mem);
+   if (need_old_upd && table->old_upd_tuplestore == NULL)
+       table->old_upd_tuplestore = tuplestore_begin_heap(false, false, work_mem);
+   if (need_new_upd && table->new_upd_tuplestore == NULL)
+       table->new_upd_tuplestore = tuplestore_begin_heap(false, false, work_mem);
+   if (need_old_del && table->old_del_tuplestore == NULL)
+       table->old_del_tuplestore = tuplestore_begin_heap(false, false, work_mem);
+   if (need_new_ins && table->new_ins_tuplestore == NULL)
+       table->new_ins_tuplestore = tuplestore_begin_heap(false, false, work_mem);
 
    CurrentResourceOwner = saveResourceOwner;
    MemoryContextSwitchTo(oldcxt);
    {
        AfterTriggersTableData *table = (AfterTriggersTableData *) lfirst(lc);
 
-       ts = table->old_tuplestore;
-       table->old_tuplestore = NULL;
+       ts = table->old_upd_tuplestore;
+       table->old_upd_tuplestore = NULL;
        if (ts)
            tuplestore_end(ts);
-       ts = table->new_tuplestore;
-       table->new_tuplestore = NULL;
+       ts = table->new_upd_tuplestore;
+       table->new_upd_tuplestore = NULL;
+       if (ts)
+           tuplestore_end(ts);
+       ts = table->old_del_tuplestore;
+       table->old_del_tuplestore = NULL;
+       if (ts)
+           tuplestore_end(ts);
+       ts = table->new_ins_tuplestore;
+       table->new_ins_tuplestore = NULL;
        if (ts)
            tuplestore_end(ts);
    }
                 newtup == NULL));
 
        if (oldtup != NULL &&
-           ((event == TRIGGER_EVENT_DELETE && delete_old_table) ||
-            (event == TRIGGER_EVENT_UPDATE && update_old_table)))
+           (event == TRIGGER_EVENT_DELETE && delete_old_table))
        {
            Tuplestorestate *old_tuplestore;
 
-           old_tuplestore = transition_capture->tcs_private->old_tuplestore;
+           old_tuplestore = transition_capture->tcs_private->old_del_tuplestore;
 
            if (map != NULL)
            {
            else
                tuplestore_puttuple(old_tuplestore, oldtup);
        }
+       if (oldtup != NULL &&
+            (event == TRIGGER_EVENT_UPDATE && update_old_table))
+       {
+           Tuplestorestate *old_tuplestore;
+
+           old_tuplestore = transition_capture->tcs_private->old_upd_tuplestore;
+
+           if (map != NULL)
+           {
+               HeapTuple   converted = do_convert_tuple(oldtup, map);
+
+               tuplestore_puttuple(old_tuplestore, converted);
+               pfree(converted);
+           }
+           else
+               tuplestore_puttuple(old_tuplestore, oldtup);
+       }
+       if (newtup != NULL &&
+           (event == TRIGGER_EVENT_INSERT && insert_new_table))
+       {
+           Tuplestorestate *new_tuplestore;
+
+           new_tuplestore = transition_capture->tcs_private->new_ins_tuplestore;
+
+           if (original_insert_tuple != NULL)
+               tuplestore_puttuple(new_tuplestore, original_insert_tuple);
+           else if (map != NULL)
+           {
+               HeapTuple   converted = do_convert_tuple(newtup, map);
+
+               tuplestore_puttuple(new_tuplestore, converted);
+               pfree(converted);
+           }
+           else
+               tuplestore_puttuple(new_tuplestore, newtup);
+       }
        if (newtup != NULL &&
-           ((event == TRIGGER_EVENT_INSERT && insert_new_table) ||
-           (event == TRIGGER_EVENT_UPDATE && update_new_table)))
+           (event == TRIGGER_EVENT_UPDATE && update_new_table))
        {
            Tuplestorestate *new_tuplestore;
 
-           new_tuplestore = transition_capture->tcs_private->new_tuplestore;
+           new_tuplestore = transition_capture->tcs_private->new_upd_tuplestore;
 
            if (original_insert_tuple != NULL)
                tuplestore_puttuple(new_tuplestore, original_insert_tuple);
 
        nodeCustom.o nodeFunctionscan.o nodeGather.o \
        nodeHash.o nodeHashjoin.o nodeIndexscan.o nodeIndexonlyscan.o \
        nodeLimit.o nodeLockRows.o nodeGatherMerge.o \
-       nodeMaterial.o nodeMergeAppend.o nodeMergejoin.o nodeModifyTable.o \
+       nodeMaterial.o nodeMergeAppend.o nodeMergejoin.o nodeMerge.o nodeModifyTable.o \
        nodeNestloop.o nodeProjectSet.o nodeRecursiveunion.o nodeResult.o \
        nodeSamplescan.o nodeSeqscan.o nodeSetOp.o nodeSort.o nodeUnique.o \
        nodeValuesscan.o \
 
 one.  For DELETE, the plan tree need only deliver a CTID column, and the
 ModifyTable node visits each of those rows and marks the row deleted.
 
+MERGE runs one generic plan that returns candidate target rows. Each row
+consists of a super-row that contains all the columns needed by any of the
+individual actions, plus a CTID and a TABLEOID junk columns. The CTID column is
+required to know if a matching target row was found or not and the TABLEOID
+column is needed to find the underlying target partition, in case when the
+target table is a partition table. If the CTID column is set we attempt to
+activate WHEN MATCHED actions, or if it is NULL then we will attempt to
+activate WHEN NOT MATCHED actions. Once we know which action is activated we
+form the final result row and apply only those changes.
+
 XXX a great deal more documentation needs to be written here...
 
 
 
        case CMD_INSERT:
        case CMD_DELETE:
        case CMD_UPDATE:
+       case CMD_MERGE:
            estate->es_output_cid = GetCurrentCommandId(true);
            break;
 
    resultRelInfo->ri_onConflictArbiterIndexes = NIL;
    resultRelInfo->ri_onConflict = NULL;
 
+   resultRelInfo->ri_mergeTargetRTI = 0;
+   resultRelInfo->ri_mergeState = (MergeState *) palloc0(sizeof (MergeState));
+
    /*
     * Partition constraint, which also includes the partition constraint of
     * all the ancestors that are partitions.  Note that it will be checked
                                 errmsg("new row violates row-level security policy for table \"%s\"",
                                        wco->relname)));
                    break;
+               case WCO_RLS_MERGE_UPDATE_CHECK:
+               case WCO_RLS_MERGE_DELETE_CHECK:
+                   if (wco->polname != NULL)
+                       ereport(ERROR,
+                               (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+                                errmsg("target row violates row-level security policy \"%s\" (USING expression) for table \"%s\"",
+                                       wco->polname, wco->relname)));
+                   else
+                       ereport(ERROR,
+                               (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+                                errmsg("target row violates row-level security policy (USING expression) for table \"%s\"",
+                                       wco->relname)));
+                   break;
                case WCO_RLS_CONFLICT_CHECK:
                    if (wco->polname != NULL)
                        ereport(ERROR,
 
    ResultRelInfo *update_rri = NULL;
    int         num_update_rri = 0,
                update_rri_index = 0;
+   bool        is_update = false;
+   bool        is_merge = false;
    PartitionTupleRouting *proute;
    int         nparts;
    ModifyTable *node = mtstate ? (ModifyTable *) mtstate->ps.plan : NULL;
 
    /* Set up details specific to the type of tuple routing we are doing. */
    if (node && node->operation == CMD_UPDATE)
+       is_update = true;
+   else if (node && node->operation == CMD_MERGE)
+       is_merge = true;
+
+   if (is_update)
    {
        update_rri = mtstate->resultRelInfo;
        num_update_rri = list_length(node->plans);
        proute->subplan_partition_offsets =
            palloc(num_update_rri * sizeof(int));
        proute->num_subplan_partition_offsets = num_update_rri;
+   }
+
 
+   if (is_update || is_merge)
+   {
        /*
         * We need an additional tuple slot for storing transient tuples that
         * are converted to the root table descriptor.
    return result;
 }
 
+/*
+ * Given OID of the partition leaf, return the index of the leaf in the
+ * partition hierarchy.
+ */
+int
+ExecFindPartitionByOid(PartitionTupleRouting *proute, Oid partoid)
+{
+   int i;
+
+   for (i = 0; i < proute->num_partitions; i++)
+   {
+       if (proute->partition_oids[i] == partoid)
+           break;
+   }
+
+   Assert(i < proute->num_partitions);
+   return i;
+}
+
 /*
  * ExecInitPartitionInfo
  *     Initialize ResultRelInfo and other information for a partition if not
                      rootrel,
                      estate->es_instrument);
 
+   leaf_part_rri->ri_PartitionLeafIndex = partidx;
+
    /*
     * Verify result relation is a valid target for an INSERT.  An UPDATE of a
     * partition-key becomes a DELETE+INSERT operation, so this check is still
    Assert(proute->partitions[partidx] == NULL);
    proute->partitions[partidx] = leaf_part_rri;
 
+   /*
+    * Initialize information about this partition that's needed to handle
+    * MERGE.
+    */
+   if (node && node->operation == CMD_MERGE)
+   {
+       TupleDesc   partrelDesc = RelationGetDescr(partrel);
+       TupleConversionMap *map = proute->parent_child_tupconv_maps[partidx];
+       int         firstVarno = mtstate->resultRelInfo[0].ri_RangeTableIndex;
+       Relation    firstResultRel = mtstate->resultRelInfo[0].ri_RelationDesc;
+
+       /*
+        * If the root parent and partition have the same tuple
+        * descriptor, just reuse the original MERGE state for partition.
+        */
+       if (map == NULL)
+       {
+           leaf_part_rri->ri_mergeState = resultRelInfo->ri_mergeState;
+       }
+       else
+       {
+           /* Convert expressions contain partition's attnos. */
+           List       *conv_tl, *conv_qual;
+           ListCell   *l;
+           List       *matchedActionStates = NIL;
+           List       *notMatchedActionStates = NIL;
+
+           foreach (l, node->mergeActionList)
+           {
+               MergeAction *action = lfirst_node(MergeAction, l);
+               MergeActionState *action_state = makeNode(MergeActionState);
+               TupleDesc   tupDesc;
+               ExprContext *econtext;
+
+               action_state->matched = action->matched;
+               action_state->commandType = action->commandType;
+
+               conv_qual = (List *) action->qual;
+               conv_qual = map_partition_varattnos(conv_qual,
+                           firstVarno, partrel,
+                           firstResultRel, NULL);
+
+               action_state->whenqual = ExecInitQual(conv_qual, &mtstate->ps);
+
+               conv_tl = (List *) action->targetList;
+               conv_tl = map_partition_varattnos(conv_tl,
+                           firstVarno, partrel,
+                           firstResultRel, NULL);
+
+               conv_tl = adjust_partition_tlist( conv_tl, map);
+
+               tupDesc = ExecTypeFromTL(conv_tl, partrelDesc->tdhasoid);
+               action_state->tupDesc = tupDesc;
+
+               /* build action projection state */
+               econtext = mtstate->ps.ps_ExprContext;
+               action_state->proj =
+                   ExecBuildProjectionInfo(conv_tl, econtext,
+                           mtstate->mt_mergeproj,
+                           &mtstate->ps,
+                           partrelDesc);
+
+               if (action_state->matched)
+                   matchedActionStates =
+                       lappend(matchedActionStates, action_state);
+               else
+                   notMatchedActionStates =
+                       lappend(notMatchedActionStates, action_state);
+           }
+           leaf_part_rri->ri_mergeState->matchedActionStates =
+               matchedActionStates;
+           leaf_part_rri->ri_mergeState->notMatchedActionStates =
+               notMatchedActionStates;
+       }
+
+       /*
+        * get_partition_dispatch_recurse() and expand_partitioned_rtentry()
+        * fetch the leaf OIDs in the same order. So we can safely derive the
+        * index of the merge target relation corresponding to this partition
+        * by simply adding partidx + 1 to the root's merge target relation.
+        */
+       leaf_part_rri->ri_mergeTargetRTI = node->mergeTargetRelation +
+           partidx + 1;
+   }
    MemoryContextSwitchTo(oldContext);
 
    return leaf_part_rri;
 
    {
        slot = ExecBRUpdateTriggers(estate, epqstate, resultRelInfo,
                                    &searchslot->tts_tuple->t_self,
-                                   NULL, slot);
+                                   NULL, slot, NULL);
 
        if (slot == NULL)       /* "do nothing" */
            skip_tuple = true;
    {
        skip_tuple = !ExecBRDeleteTriggers(estate, epqstate, resultRelInfo,
                                           &searchslot->tts_tuple->t_self,
-                                          NULL);
+                                          NULL, NULL);
    }
 
    if (!skip_tuple)
 
 #include "commands/trigger.h"
 #include "executor/execPartition.h"
 #include "executor/executor.h"
+#include "executor/nodeMerge.h"
 #include "executor/nodeModifyTable.h"
 #include "foreign/fdwapi.h"
 #include "miscadmin.h"
                     EState *estate,
                     bool canSetTag,
                     TupleTableSlot **returning);
-static TupleTableSlot *ExecPrepareTupleRouting(ModifyTableState *mtstate,
-                       EState *estate,
-                       PartitionTupleRouting *proute,
-                       ResultRelInfo *targetRelInfo,
-                       TupleTableSlot *slot);
 static ResultRelInfo *getTargetResultRelInfo(ModifyTableState *node);
 static void ExecSetupChildParentMapForTcs(ModifyTableState *mtstate);
 static void ExecSetupChildParentMapForSubplan(ModifyTableState *mtstate);
 static TupleConversionMap *tupconv_map_for_subplan(ModifyTableState *node,
                        int whichplan);
 
+/* flags for mt_merge_subcommands */
+#define MERGE_INSERT   0x01
+#define MERGE_UPDATE   0x02
+#define MERGE_DELETE   0x04
+
 /*
  * Verify that the tuples to be produced by INSERT or UPDATE match the
  * target relation's rowtype
  *     Returns RETURNING result if any, otherwise NULL.
  * ----------------------------------------------------------------
  */
-static TupleTableSlot *
+extern TupleTableSlot *
 ExecInsert(ModifyTableState *mtstate,
           TupleTableSlot *slot,
           TupleTableSlot *planSlot,
           EState *estate,
+          MergeActionState *actionState,
           bool canSetTag)
 {
    HeapTuple   tuple;
         * partition, we should instead check UPDATE policies, because we are
         * executing policies defined on the target table, and not those
         * defined on the child partitions.
+        *
+        * If we're running MERGE, we refer to the action that we're executing
+        * to know if we're doing an INSERT or UPDATE to a partition table.
         */
-       wco_kind = (mtstate->operation == CMD_UPDATE) ?
-           WCO_RLS_UPDATE_CHECK : WCO_RLS_INSERT_CHECK;
+       if (mtstate->operation == CMD_UPDATE)
+           wco_kind = WCO_RLS_UPDATE_CHECK;
+       else if (mtstate->operation == CMD_MERGE)
+           wco_kind = (actionState->commandType == CMD_UPDATE) ?
+               WCO_RLS_UPDATE_CHECK : WCO_RLS_INSERT_CHECK;
+       else
+           wco_kind = WCO_RLS_INSERT_CHECK;
 
        /*
         * ExecWithCheckOptions() will skip any WCOs which are not of the kind
  *     passed to foreign table triggers; it is NULL when the foreign
  *     table has no relevant triggers.
  *
+ *     MERGE passes actionState of the action it's currently executing;
+ *     regular DELETE passes NULL. This is used by ExecDelete to know if it's
+ *     being called from MERGE or regular DELETE operation.
+ *
+ *     If the DELETE fails because the tuple is concurrently updated/deleted
+ *     by this or some other transaction, hufdp is filled with the reason as
+ *     well as other important information. Currently only MERGE needs this
+ *     information.
+ *
  *     Returns RETURNING result if any, otherwise NULL.
  * ----------------------------------------------------------------
  */
-static TupleTableSlot *
+TupleTableSlot *
 ExecDelete(ModifyTableState *mtstate,
           ItemPointer tupleid,
           HeapTuple oldtuple,
           EState *estate,
           bool *tupleDeleted,
           bool processReturning,
+          HeapUpdateFailureData *hufdp,
+          MergeActionState *actionState,
           bool canSetTag)
 {
    ResultRelInfo *resultRelInfo;
    if (tupleDeleted)
        *tupleDeleted = false;
 
+   /*
+    * Initialize hufdp. Since the caller is only interested in the failure
+    * status, initialize with the state that is used to indicate successful
+    * operation.
+    */
+   if (hufdp)
+       hufdp->result = HeapTupleMayBeUpdated;
+
    /*
     * get information on the (current) result relation
     */
        bool        dodelete;
 
        dodelete = ExecBRDeleteTriggers(estate, epqstate, resultRelInfo,
-                                       tupleid, oldtuple);
+                                       tupleid, oldtuple, hufdp);
 
        if (!dodelete)          /* "do nothing" */
            return NULL;
                             estate->es_crosscheck_snapshot,
                             true /* wait for commit */ ,
                             &hufd);
+
+       /*
+        * Copy the necessary information, if the caller has asked for it. We
+        * must do this irrespective of whether the tuple was updated or
+        * deleted.
+        */
+       if (hufdp)
+           *hufdp = hufd;
+
        switch (result)
        {
            case HeapTupleSelfUpdated:
                             errmsg("tuple to be updated was already modified by an operation triggered by the current command"),
                             errhint("Consider using an AFTER trigger instead of a BEFORE trigger to propagate changes to other rows.")));
 
-               /* Else, already deleted by self; nothing to do */
+               /*
+                * Else, already deleted by self; nothing to do but inform
+                * MERGE about it anyways so that it can take necessary
+                * action.
+                */
                return NULL;
 
            case HeapTupleMayBeUpdated:
                    ereport(ERROR,
                            (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
                             errmsg("could not serialize access due to concurrent update")));
+
                if (!ItemPointerEquals(tupleid, &hufd.ctid))
                {
                    TupleTableSlot *epqslot;
 
+                   /*
+                    * If we're executing MERGE, then the onus of running
+                    * EvalPlanQual() and handling its outcome lies with the
+                    * caller.
+                    */
+                   if (actionState != NULL)
+                       return NULL;
+
+                   /* Normal DELETE path.  */
                    epqslot = EvalPlanQual(estate,
                                           epqstate,
                                           resultRelationDesc,
-                                          resultRelInfo->ri_RangeTableIndex,
+                                          GetEPQRangeTableIndex(resultRelInfo),
                                           LockTupleExclusive,
                                           &hufd.ctid,
                                           hufd.xmax);
                        goto ldelete;
                    }
                }
-               /* tuple already deleted; nothing to do */
+
+               /*
+                * tuple already deleted; nothing to do. But MERGE might want
+                * to handle it differently. We've already filled-in hufdp
+                * with sufficient information for MERGE to look at.
+                */
                return NULL;
 
            default:
  *     foreign table triggers; it is NULL when the foreign table has
  *     no relevant triggers.
  *
+ *     MERGE passes actionState of the action it's currently executing;
+ *     regular UPDATE passes NULL. This is used by ExecUpdate to know if it's
+ *     being called from MERGE or regular UPDATE operation. ExecUpdate may
+ *     pass this information to ExecInsert if it ends up running DELETE+INSERT
+ *     for partition key updates.
+ *
+ *     If the UPDATE fails because the tuple is concurrently updated/deleted
+ *     by this or some other transaction, hufdp is filled with the reason as
+ *     well as other important information. Currently only MERGE needs this
+ *     information.
+ *
  *     Returns RETURNING result if any, otherwise NULL.
  * ----------------------------------------------------------------
  */
-static TupleTableSlot *
+extern TupleTableSlot *
 ExecUpdate(ModifyTableState *mtstate,
           ItemPointer tupleid,
           HeapTuple oldtuple,
           TupleTableSlot *planSlot,
           EPQState *epqstate,
           EState *estate,
+          bool *tuple_updated,
+          HeapUpdateFailureData *hufdp,
+          MergeActionState *actionState,
           bool canSetTag)
 {
    HeapTuple   tuple;
    if (IsBootstrapProcessingMode())
        elog(ERROR, "cannot UPDATE during bootstrap");
 
+   if (tuple_updated)
+       *tuple_updated = false;
+
+   /*
+    * Initialize hufdp. Since the caller is only interested in the failure
+    * status, initialize with the state that is used to indicate successful
+    * operation.
+    */
+   if (hufdp)
+       hufdp->result = HeapTupleMayBeUpdated;
+
    /*
     * get the heap tuple out of the tuple table slot, making sure we have a
     * writable copy
        resultRelInfo->ri_TrigDesc->trig_update_before_row)
    {
        slot = ExecBRUpdateTriggers(estate, epqstate, resultRelInfo,
-                                   tupleid, oldtuple, slot);
+                                   tupleid, oldtuple, slot, hufdp);
 
        if (slot == NULL)       /* "do nothing" */
            return NULL;
    }
    else
    {
-       LockTupleMode lockmode;
        bool        partition_constraint_failed;
 
        /*
             * Row movement, part 1.  Delete the tuple, but skip RETURNING
             * processing. We want to return rows from INSERT.
             */
-           ExecDelete(mtstate, tupleid, oldtuple, planSlot, epqstate, estate,
-                      &tuple_deleted, false, false);
+           ExecDelete(mtstate, tupleid, oldtuple, planSlot, epqstate,
+                      estate, &tuple_deleted, false, hufdp, NULL,
+                      false);
 
            /*
             * For some reason if DELETE didn't happen (e.g. trigger prevented
                saved_tcs_map = mtstate->mt_transition_capture->tcs_map;
 
            /*
-            * resultRelInfo is one of the per-subplan resultRelInfos.  So we
-            * should convert the tuple into root's tuple descriptor, since
-            * ExecInsert() starts the search from root.  The tuple conversion
-            * map list is in the order of mtstate->resultRelInfo[], so to
-            * retrieve the one for this resultRel, we need to know the
-            * position of the resultRel in mtstate->resultRelInfo[].
+            * We should convert the tuple into root's tuple descriptor, since
+            * ExecInsert() starts the search from root. To do that, we need to
+            * retrieve the tuple conversion map for this resultRelInfo.
+            *
+            * If we're running MERGE then resultRelInfo is per-partition
+            * resultRelInfo as initialized in ExecInitPartitionInfo(). Note
+            * that we don't expand inheritance for the resultRelation in case
+            * of MERGE and hence there is just one subplan. Whereas for
+            * regular UPDATE, resultRelInfo is one of the per-subplan
+            * resultRelInfos. In either case the position of this partition in
+            * tracked in ri_PartitionLeafIndex;
+            *
+            * Retrieve the map either by looking at the resultRelInfo's
+            * position in mtstate->resultRelInfo[] (for UPDATE) or by simply
+            * using the ri_PartitionLeafIndex value (for MERGE).
             */
-           map_index = resultRelInfo - mtstate->resultRelInfo;
-           Assert(map_index >= 0 && map_index < mtstate->mt_nplans);
-           tupconv_map = tupconv_map_for_subplan(mtstate, map_index);
+           if (mtstate->operation == CMD_MERGE)
+           {
+               map_index = resultRelInfo->ri_PartitionLeafIndex;
+               Assert(mtstate->rootResultRelInfo == NULL);
+               tupconv_map = TupConvMapForLeaf(proute,
+                               mtstate->resultRelInfo,
+                               map_index);
+           }
+           else
+           {
+               map_index = resultRelInfo - mtstate->resultRelInfo;
+               Assert(map_index >= 0 && map_index < mtstate->mt_nplans);
+               tupconv_map = tupconv_map_for_subplan(mtstate, map_index);
+           }
            tuple = ConvertPartitionTupleSlot(tupconv_map,
                                              tuple,
                                              proute->root_tuple_slot,
             * Prepare for tuple routing, making it look like we're inserting
             * into the root.
             */
-           Assert(mtstate->rootResultRelInfo != NULL);
            slot = ExecPrepareTupleRouting(mtstate, estate, proute,
-                                          mtstate->rootResultRelInfo, slot);
+                                          getTargetResultRelInfo(mtstate),
+                                          slot);
 
            ret_slot = ExecInsert(mtstate, slot, planSlot,
-                                 estate, canSetTag);
+                                 estate, actionState, canSetTag);
+
+           /* Update is successful. */
+           if (tuple_updated)
+               *tuple_updated = true;
 
            /* Revert ExecPrepareTupleRouting's node change. */
            estate->es_result_relation_info = resultRelInfo;
                             estate->es_output_cid,
                             estate->es_crosscheck_snapshot,
                             true /* wait for commit */ ,
-                            &hufd, &lockmode);
+                            &hufd);
+
+       /*
+        * Copy the necessary information, if the caller has asked for it. We
+        * must do this irrespective of whether the tuple was updated or
+        * deleted.
+        */
+       if (hufdp)
+           *hufdp = hufd;
+
        switch (result)
        {
            case HeapTupleSelfUpdated:
                    ereport(ERROR,
                            (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
                             errmsg("could not serialize access due to concurrent update")));
+
                if (!ItemPointerEquals(tupleid, &hufd.ctid))
                {
                    TupleTableSlot *epqslot;
 
+                   /*
+                    * If we're executing MERGE, then the onus of running
+                    * EvalPlanQual() and handling its outcome lies with the
+                    * caller.
+                    */
+                   if (actionState != NULL)
+                       return NULL;
+
+                   /* Regular UPDATE path. */
                    epqslot = EvalPlanQual(estate,
                                           epqstate,
                                           resultRelationDesc,
-                                          resultRelInfo->ri_RangeTableIndex,
-                                          lockmode,
+                                          GetEPQRangeTableIndex(resultRelInfo),
+                                          hufd.lockmode,
                                           &hufd.ctid,
                                           hufd.xmax);
                    if (!TupIsNull(epqslot))
                    {
                        *tupleid = hufd.ctid;
+                       /* Normal UPDATE path */
                        slot = ExecFilterJunk(resultRelInfo->ri_junkFilter, epqslot);
                        tuple = ExecMaterializeSlot(slot);
                        goto lreplace;
                    }
                }
-               /* tuple already deleted; nothing to do */
+
+               /*
+                * tuple already deleted; nothing to do. But MERGE might want
+                * to handle it differently. We've already filled-in hufdp
+                * with sufficient information for MERGE to look at.
+                */
                return NULL;
 
            default:
                                                   estate, false, NULL, NIL);
    }
 
+   if (tuple_updated)
+       *tuple_updated = true;
+
    if (canSetTag)
        (estate->es_processed)++;
 
             * there's no historical behavior to break.
             *
             * It is the user's responsibility to prevent this situation from
-            * occurring.  These problems are why SQL-2003 similarly specifies
-            * that for SQL MERGE, an exception must be raised in the event of
-            * an attempt to update the same row twice.
+            * occurring.  These problems are why SQL Standard similarly
+            * specifies that for SQL MERGE, an exception must be raised in
+            * the event of an attempt to update the same row twice.
             */
            if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetXmin(tuple.t_data)))
                ereport(ERROR,
    *returning = ExecUpdate(mtstate, &tuple.t_self, NULL,
                            mtstate->mt_conflproj, planSlot,
                            &mtstate->mt_epqstate, mtstate->ps.state,
-                           canSetTag);
+                           NULL, NULL, NULL, canSetTag);
 
    ReleaseBuffer(buffer);
    return true;
        case CMD_DELETE:
            ExecBSDeleteTriggers(node->ps.state, resultRelInfo);
            break;
+       case CMD_MERGE:
+           if (node->mt_merge_subcommands & MERGE_INSERT)
+               ExecBSInsertTriggers(node->ps.state, resultRelInfo);
+           if (node->mt_merge_subcommands & MERGE_UPDATE)
+               ExecBSUpdateTriggers(node->ps.state, resultRelInfo);
+           if (node->mt_merge_subcommands & MERGE_DELETE)
+               ExecBSDeleteTriggers(node->ps.state, resultRelInfo);
+           break;
        default:
            elog(ERROR, "unknown operation");
            break;
            ExecASDeleteTriggers(node->ps.state, resultRelInfo,
                                 node->mt_transition_capture);
            break;
+       case CMD_MERGE:
+           if (node->mt_merge_subcommands & MERGE_DELETE)
+               ExecASDeleteTriggers(node->ps.state, resultRelInfo,
+                                    node->mt_transition_capture);
+           if (node->mt_merge_subcommands & MERGE_UPDATE)
+               ExecASUpdateTriggers(node->ps.state, resultRelInfo,
+                                    node->mt_transition_capture);
+           if (node->mt_merge_subcommands & MERGE_INSERT)
+               ExecASInsertTriggers(node->ps.state, resultRelInfo,
+                                    node->mt_transition_capture);
+           break;
        default:
            elog(ERROR, "unknown operation");
            break;
  *
  * Returns a slot holding the tuple of the partition rowtype.
  */
-static TupleTableSlot *
+TupleTableSlot *
 ExecPrepareTupleRouting(ModifyTableState *mtstate,
                        EState *estate,
                        PartitionTupleRouting *proute,
        {
            /* advance to next subplan if any */
            node->mt_whichplan++;
+
            if (node->mt_whichplan < node->mt_nplans)
            {
                resultRelInfo++;
        EvalPlanQualSetSlot(&node->mt_epqstate, planSlot);
        slot = planSlot;
 
+       if (operation == CMD_MERGE)
+       {
+           ExecMerge(node, estate, slot, junkfilter, resultRelInfo);
+           continue;
+       }
+
        tupleid = NULL;
        oldtuple = NULL;
        if (junkfilter != NULL)
                    slot = ExecPrepareTupleRouting(node, estate, proute,
                                                   resultRelInfo, slot);
                slot = ExecInsert(node, slot, planSlot,
-                                 estate, node->canSetTag);
+                                 estate, NULL, node->canSetTag);
                /* Revert ExecPrepareTupleRouting's state change. */
                if (proute)
                    estate->es_result_relation_info = resultRelInfo;
                break;
            case CMD_UPDATE:
                slot = ExecUpdate(node, tupleid, oldtuple, slot, planSlot,
-                                 &node->mt_epqstate, estate, node->canSetTag);
+                                 &node->mt_epqstate, estate,
+                                 NULL, NULL, NULL, node->canSetTag);
                break;
            case CMD_DELETE:
                slot = ExecDelete(node, tupleid, oldtuple, planSlot,
                                  &node->mt_epqstate, estate,
-                                 NULL, true, node->canSetTag);
+                                 NULL, true, NULL, NULL, node->canSetTag);
                break;
            default:
                elog(ERROR, "unknown operation");
    saved_resultRelInfo = estate->es_result_relation_info;
 
    resultRelInfo = mtstate->resultRelInfo;
+
+   /*
+    * mergeTargetRelation must be set if we're running MERGE and mustn't be
+    * set if we're not.
+    */
+   Assert(operation != CMD_MERGE || node->mergeTargetRelation > 0);
+   Assert(operation == CMD_MERGE || node->mergeTargetRelation == 0);
+
+   resultRelInfo->ri_mergeTargetRTI = node->mergeTargetRelation;
+
    i = 0;
    foreach(l, node->plans)
    {
     * partition key.
     */
    if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE &&
-       (operation == CMD_INSERT || update_tuple_routing_needed))
+       (operation == CMD_INSERT || operation == CMD_MERGE ||
+        update_tuple_routing_needed))
        mtstate->mt_partition_tuple_routing =
                        ExecSetupPartitionTupleRouting(mtstate, rel);
 
    if (!(eflags & EXEC_FLAG_EXPLAIN_ONLY))
        ExecSetupTransitionCaptureState(mtstate, estate);
 
+   /*
+    * If we are doing MERGE then setup child-parent mapping. This will be
+    * required in case we end up doing a partition-key update, triggering a
+    * tuple routing.
+    */
+   if (mtstate->operation == CMD_MERGE &&
+       mtstate->mt_partition_tuple_routing != NULL)
+       ExecSetupChildParentMapForLeaf(mtstate->mt_partition_tuple_routing);
+
    /*
     * Construct mapping from each of the per-subplan partition attnos to the
     * root attno.  This is required when during update row movement the tuple
        }
    }
 
+   resultRelInfo = mtstate->resultRelInfo;
+
+   if (node->mergeActionList)
+   {
+       ListCell   *l;
+       ExprContext *econtext;
+       List       *mergeMatchedActionStates = NIL;
+       List       *mergeNotMatchedActionStates = NIL;
+       TupleDesc   relationDesc = resultRelInfo->ri_RelationDesc->rd_att;
+
+       mtstate->mt_merge_subcommands = 0;
+
+       if (mtstate->ps.ps_ExprContext == NULL)
+           ExecAssignExprContext(estate, &mtstate->ps);
+
+       econtext = mtstate->ps.ps_ExprContext;
+
+       /* initialize slot for the existing tuple */
+       Assert(mtstate->mt_existing == NULL);
+       mtstate->mt_existing =
+           ExecInitExtraTupleSlot(mtstate->ps.state,
+                                  mtstate->mt_partition_tuple_routing ?
+                                  NULL : relationDesc);
+
+       /* initialize slot for merge actions */
+       Assert(mtstate->mt_mergeproj == NULL);
+       mtstate->mt_mergeproj =
+           ExecInitExtraTupleSlot(mtstate->ps.state,
+                                  mtstate->mt_partition_tuple_routing ?
+                                  NULL : relationDesc);
+
+       /*
+        * Create a MergeActionState for each action on the mergeActionList
+        * and add it to either a list of matched actions or not-matched
+        * actions.
+        */
+       foreach(l, node->mergeActionList)
+       {
+           MergeAction *action = (MergeAction *) lfirst(l);
+           MergeActionState *action_state = makeNode(MergeActionState);
+           TupleDesc   tupDesc;
+
+           action_state->matched = action->matched;
+           action_state->commandType = action->commandType;
+           action_state->whenqual = ExecInitQual((List *) action->qual,
+                   &mtstate->ps);
+
+           /* create target slot for this action's projection */
+           tupDesc = ExecTypeFromTL((List *) action->targetList,
+                   resultRelInfo->ri_RelationDesc->rd_rel->relhasoids);
+           action_state->tupDesc = tupDesc;
+
+           /* build action projection state */
+           action_state->proj =
+               ExecBuildProjectionInfo(action->targetList, econtext,
+                       mtstate->mt_mergeproj, &mtstate->ps,
+                       resultRelInfo->ri_RelationDesc->rd_att);
+
+           /*
+            * We create two lists - one for WHEN MATCHED actions and one
+            * for WHEN NOT MATCHED actions - and stick the
+            * MergeActionState into the appropriate list.
+            */
+           if (action_state->matched)
+               mergeMatchedActionStates =
+                   lappend(mergeMatchedActionStates, action_state);
+           else
+               mergeNotMatchedActionStates =
+                   lappend(mergeNotMatchedActionStates, action_state);
+
+           switch (action->commandType)
+           {
+               case CMD_INSERT:
+                   ExecCheckPlanOutput(resultRelInfo->ri_RelationDesc,
+                                       action->targetList);
+                   mtstate->mt_merge_subcommands |= MERGE_INSERT;
+                   break;
+               case CMD_UPDATE:
+                   ExecCheckPlanOutput(resultRelInfo->ri_RelationDesc,
+                                       action->targetList);
+                   mtstate->mt_merge_subcommands |= MERGE_UPDATE;
+                   break;
+               case CMD_DELETE:
+                   mtstate->mt_merge_subcommands |= MERGE_DELETE;
+                   break;
+               case CMD_NOTHING:
+                   break;
+               default:
+                   elog(ERROR, "unknown operation");
+                   break;
+           }
+
+           resultRelInfo->ri_mergeState->matchedActionStates =
+                       mergeMatchedActionStates;
+           resultRelInfo->ri_mergeState->notMatchedActionStates =
+                       mergeNotMatchedActionStates;
+
+       }
+   }
+
    /* select first subplan */
    mtstate->mt_whichplan = 0;
    subplan = (Plan *) linitial(node->plans);
     * --- no need to look first.  Typically, this will be a 'ctid' or
     * 'wholerow' attribute, but in the case of a foreign data wrapper it
     * might be a set of junk attributes sufficient to identify the remote
-    * row.
+    * row. We follow this logic for MERGE, so it always has a junk attributes.
     *
     * If there are multiple result relations, each one needs its own junk
     * filter.  Note multiple rels are only possible for UPDATE/DELETE, so we
                break;
            case CMD_UPDATE:
            case CMD_DELETE:
+           case CMD_MERGE:
                junk_filter_needed = true;
                break;
            default:
                JunkFilter *j;
 
                subplan = mtstate->mt_plans[i]->plan;
+
                if (operation == CMD_INSERT || operation == CMD_UPDATE)
                    ExecCheckPlanOutput(resultRelInfo->ri_RelationDesc,
                                        subplan->targetlist);
                                       resultRelInfo->ri_RelationDesc->rd_att->tdhasoid,
                                       ExecInitExtraTupleSlot(estate, NULL));
 
-               if (operation == CMD_UPDATE || operation == CMD_DELETE)
+               if (operation == CMD_UPDATE ||
+                   operation == CMD_DELETE ||
+                   operation == CMD_MERGE)
                {
                    /* For UPDATE/DELETE, find the appropriate junk attr now */
                    char        relkind;
                        j->jf_junkAttNo = ExecFindJunkAttribute(j, "ctid");
                        if (!AttributeNumberIsValid(j->jf_junkAttNo))
                            elog(ERROR, "could not find junk ctid column");
+
+                       if (operation == CMD_MERGE &&
+                           relkind == RELKIND_PARTITIONED_TABLE)
+                       {
+                           j->jf_otherJunkAttNo = ExecFindJunkAttribute(j, "tableoid");
+                           if (!AttributeNumberIsValid(j->jf_otherJunkAttNo))
+                               elog(ERROR, "could not find junk tableoid column");
+
+                       }
                    }
                    else if (relkind == RELKIND_FOREIGN_TABLE)
                    {
 
            else
                res = SPI_OK_UPDATE;
            break;
+       case CMD_MERGE:
+           res = SPI_OK_MERGE;
+           break;
        default:
            return SPI_ERROR_OPUNKNOWN;
    }
 
    COPY_NODE_FIELD(partitioned_rels);
    COPY_SCALAR_FIELD(partColsUpdated);
    COPY_NODE_FIELD(resultRelations);
+   COPY_SCALAR_FIELD(mergeTargetRelation);
    COPY_SCALAR_FIELD(resultRelIndex);
    COPY_SCALAR_FIELD(rootResultRelIndex);
    COPY_NODE_FIELD(plans);
    COPY_NODE_FIELD(onConflictWhere);
    COPY_SCALAR_FIELD(exclRelRTI);
    COPY_NODE_FIELD(exclRelTlist);
+   COPY_NODE_FIELD(mergeSourceTargetList);
+   COPY_NODE_FIELD(mergeActionList);
 
    return newnode;
 }
    COPY_NODE_FIELD(setOperations);
    COPY_NODE_FIELD(constraintDeps);
    COPY_NODE_FIELD(withCheckOptions);
+   COPY_SCALAR_FIELD(mergeTarget_relation);
+   COPY_NODE_FIELD(mergeSourceTargetList);
+   COPY_NODE_FIELD(mergeActionList);
    COPY_LOCATION_FIELD(stmt_location);
    COPY_LOCATION_FIELD(stmt_len);
 
    return newnode;
 }
 
+static MergeStmt *
+_copyMergeStmt(const MergeStmt *from)
+{
+   MergeStmt  *newnode = makeNode(MergeStmt);
+
+   COPY_NODE_FIELD(relation);
+   COPY_NODE_FIELD(source_relation);
+   COPY_NODE_FIELD(join_condition);
+   COPY_NODE_FIELD(mergeActionList);
+
+   return newnode;
+}
+
+static MergeAction *
+_copyMergeAction(const MergeAction *from)
+{
+   MergeAction *newnode = makeNode(MergeAction);
+
+   COPY_SCALAR_FIELD(matched);
+   COPY_SCALAR_FIELD(commandType);
+   COPY_NODE_FIELD(condition);
+   COPY_NODE_FIELD(qual);
+   COPY_NODE_FIELD(stmt);
+   COPY_NODE_FIELD(targetList);
+
+   return newnode;
+}
+
 static SelectStmt *
 _copySelectStmt(const SelectStmt *from)
 {
        case T_UpdateStmt:
            retval = _copyUpdateStmt(from);
            break;
+       case T_MergeStmt:
+           retval = _copyMergeStmt(from);
+           break;
+       case T_MergeAction:
+           retval = _copyMergeAction(from);
+           break;
        case T_SelectStmt:
            retval = _copySelectStmt(from);
            break;
 
    COMPARE_NODE_FIELD(setOperations);
    COMPARE_NODE_FIELD(constraintDeps);
    COMPARE_NODE_FIELD(withCheckOptions);
+   COMPARE_NODE_FIELD(mergeSourceTargetList);
+   COMPARE_NODE_FIELD(mergeActionList);
    COMPARE_LOCATION_FIELD(stmt_location);
    COMPARE_LOCATION_FIELD(stmt_len);
 
    return true;
 }
 
+static bool
+_equalMergeStmt(const MergeStmt *a, const MergeStmt *b)
+{
+   COMPARE_NODE_FIELD(relation);
+   COMPARE_NODE_FIELD(source_relation);
+   COMPARE_NODE_FIELD(join_condition);
+   COMPARE_NODE_FIELD(mergeActionList);
+
+   return true;
+}
+
+static bool
+_equalMergeAction(const MergeAction *a, const MergeAction *b)
+{
+   COMPARE_SCALAR_FIELD(matched);
+   COMPARE_SCALAR_FIELD(commandType);
+   COMPARE_NODE_FIELD(condition);
+   COMPARE_NODE_FIELD(qual);
+   COMPARE_NODE_FIELD(stmt);
+   COMPARE_NODE_FIELD(targetList);
+
+   return true;
+}
+
 static bool
 _equalSelectStmt(const SelectStmt *a, const SelectStmt *b)
 {
        case T_UpdateStmt:
            retval = _equalUpdateStmt(a, b);
            break;
+       case T_MergeStmt:
+           retval = _equalMergeStmt(a, b);
+           break;
+       case T_MergeAction:
+           retval = _equalMergeAction(a, b);
+           break;
        case T_SelectStmt:
            retval = _equalSelectStmt(a, b);
            break;
 
                    return true;
            }
            break;
+       case T_MergeAction:
+           {
+               MergeAction *action = (MergeAction *) node;
+
+               if (walker(action->targetList, context))
+                   return true;
+               if (walker(action->qual, context))
+                   return true;
+           }
+           break;
        case T_JoinExpr:
            {
                JoinExpr   *join = (JoinExpr *) node;
        return true;
    if (walker((Node *) query->onConflict, context))
        return true;
+   if (walker((Node *) query->mergeSourceTargetList, context))
+       return true;
+   if (walker((Node *) query->mergeActionList, context))
+       return true;
    if (walker((Node *) query->returningList, context))
        return true;
    if (walker((Node *) query->jointree, context))
                return (Node *) newnode;
            }
            break;
+       case T_MergeAction:
+           {
+               MergeAction *action = (MergeAction *) node;
+               MergeAction *newnode;
+
+               FLATCOPY(newnode, action, MergeAction);
+               MUTATE(newnode->qual, action->qual, Node *);
+               MUTATE(newnode->targetList, action->targetList, List *);
+
+               return (Node *) newnode;
+           }
+           break;
        case T_JoinExpr:
            {
                JoinExpr   *join = (JoinExpr *) node;
    MUTATE(query->targetList, query->targetList, List *);
    MUTATE(query->withCheckOptions, query->withCheckOptions, List *);
    MUTATE(query->onConflict, query->onConflict, OnConflictExpr *);
+   MUTATE(query->mergeSourceTargetList, query->mergeSourceTargetList, List *);
+   MUTATE(query->mergeActionList, query->mergeActionList, List *);
    MUTATE(query->returningList, query->returningList, List *);
    MUTATE(query->jointree, query->jointree, FromExpr *);
    MUTATE(query->setOperations, query->setOperations, Node *);
  * boundaries: we descend to everything that's possibly interesting.
  *
  * Currently, the node type coverage here extends only to DML statements
- * (SELECT/INSERT/UPDATE/DELETE) and nodes that can appear in them, because
- * this is used mainly during analysis of CTEs, and only DML statements can
- * appear in CTEs.
+ * (SELECT/INSERT/UPDATE/DELETE/MERGE) and nodes that can appear in them,
+ * because this is used mainly during analysis of CTEs, and only DML
+ * statements can appear in CTEs.
  */
 bool
 raw_expression_tree_walker(Node *node,
                    return true;
            }
            break;
+       case T_MergeStmt:
+           {
+               MergeStmt  *stmt = (MergeStmt *) node;
+
+               if (walker(stmt->relation, context))
+                   return true;
+               if (walker(stmt->source_relation, context))
+                   return true;
+               if (walker(stmt->join_condition, context))
+                   return true;
+               if (walker(stmt->mergeActionList, context))
+                   return true;
+           }
+           break;
+       case T_MergeAction:
+           {
+               MergeAction *action = (MergeAction *) node;
+
+               if (walker(action->targetList, context))
+                   return true;
+               if (walker(action->qual, context))
+                   return true;
+           }
+           break;
        case T_SelectStmt:
            {
                SelectStmt *stmt = (SelectStmt *) node;
 
    WRITE_NODE_FIELD(partitioned_rels);
    WRITE_BOOL_FIELD(partColsUpdated);
    WRITE_NODE_FIELD(resultRelations);
+   WRITE_INT_FIELD(mergeTargetRelation);
    WRITE_INT_FIELD(resultRelIndex);
    WRITE_INT_FIELD(rootResultRelIndex);
    WRITE_NODE_FIELD(plans);
    WRITE_NODE_FIELD(onConflictWhere);
    WRITE_UINT_FIELD(exclRelRTI);
    WRITE_NODE_FIELD(exclRelTlist);
+   WRITE_NODE_FIELD(mergeSourceTargetList);
+   WRITE_NODE_FIELD(mergeActionList);
+}
+
+static void
+_outMergeAction(StringInfo str, const MergeAction *node)
+{
+   WRITE_NODE_TYPE("MERGEACTION");
+
+   WRITE_BOOL_FIELD(matched);
+   WRITE_ENUM_FIELD(commandType, CmdType);
+   WRITE_NODE_FIELD(condition);
+   WRITE_NODE_FIELD(qual);
+   WRITE_NODE_FIELD(stmt);
+   WRITE_NODE_FIELD(targetList);
 }
 
 static void
    WRITE_NODE_FIELD(partitioned_rels);
    WRITE_BOOL_FIELD(partColsUpdated);
    WRITE_NODE_FIELD(resultRelations);
+   WRITE_INT_FIELD(mergeTargetRelation);
    WRITE_NODE_FIELD(subpaths);
    WRITE_NODE_FIELD(subroots);
    WRITE_NODE_FIELD(withCheckOptionLists);
    WRITE_NODE_FIELD(rowMarks);
    WRITE_NODE_FIELD(onconflict);
    WRITE_INT_FIELD(epqParam);
+   WRITE_NODE_FIELD(mergeSourceTargetList);
+   WRITE_NODE_FIELD(mergeActionList);
 }
 
 static void
    WRITE_NODE_FIELD(setOperations);
    WRITE_NODE_FIELD(constraintDeps);
    /* withCheckOptions intentionally omitted, see comment in parsenodes.h */
+   WRITE_INT_FIELD(mergeTarget_relation);
+   WRITE_NODE_FIELD(mergeSourceTargetList);
+   WRITE_NODE_FIELD(mergeActionList);
    WRITE_LOCATION_FIELD(stmt_location);
    WRITE_LOCATION_FIELD(stmt_len);
 }
            case T_ModifyTable:
                _outModifyTable(str, obj);
                break;
+           case T_MergeAction:
+               _outMergeAction(str, obj);
+               break;
            case T_Append:
                _outAppend(str, obj);
                break;
 
    READ_NODE_FIELD(setOperations);
    READ_NODE_FIELD(constraintDeps);
    /* withCheckOptions intentionally omitted, see comment in parsenodes.h */
+   READ_INT_FIELD(mergeTarget_relation);
+   READ_NODE_FIELD(mergeSourceTargetList);
+   READ_NODE_FIELD(mergeActionList);
    READ_LOCATION_FIELD(stmt_location);
    READ_LOCATION_FIELD(stmt_len);
 
    READ_NODE_FIELD(partitioned_rels);
    READ_BOOL_FIELD(partColsUpdated);
    READ_NODE_FIELD(resultRelations);
+   READ_INT_FIELD(mergeTargetRelation);
    READ_INT_FIELD(resultRelIndex);
    READ_INT_FIELD(rootResultRelIndex);
    READ_NODE_FIELD(plans);
    READ_NODE_FIELD(onConflictWhere);
    READ_UINT_FIELD(exclRelRTI);
    READ_NODE_FIELD(exclRelTlist);
+   READ_NODE_FIELD(mergeSourceTargetList);
+   READ_NODE_FIELD(mergeActionList);
+
+   READ_DONE();
+}
+
+/*
+ * _readMergeAction
+ */
+static MergeAction *
+_readMergeAction(void)
+{
+   READ_LOCALS(MergeAction);
+
+   READ_BOOL_FIELD(matched);
+   READ_ENUM_FIELD(commandType, CmdType);
+   READ_NODE_FIELD(condition);
+   READ_NODE_FIELD(qual);
+   READ_NODE_FIELD(stmt);
+   READ_NODE_FIELD(targetList);
 
    READ_DONE();
 }
        return_value = _readProjectSet();
    else if (MATCH("MODIFYTABLE", 11))
        return_value = _readModifyTable();
+   else if (MATCH("MERGEACTION", 11))
+       return_value = _readMergeAction();
    else if (MATCH("APPEND", 6))
        return_value = _readAppend();
    else if (MATCH("MERGEAPPEND", 11))
 
                 CmdType operation, bool canSetTag,
                 Index nominalRelation, List *partitioned_rels,
                 bool partColsUpdated,
-                List *resultRelations, List *subplans,
+                List *resultRelations,
+                Index mergeTargetRelation,
+                List *subplans,
                 List *withCheckOptionLists, List *returningLists,
-                List *rowMarks, OnConflictExpr *onconflict, int epqParam);
+                List *rowMarks, OnConflictExpr *onconflict,
+                List *mergeSourceTargetList,
+                List *mergeActionList, int epqParam);
 static GatherMerge *create_gather_merge_plan(PlannerInfo *root,
                         GatherMergePath *best_path);
 
                            best_path->partitioned_rels,
                            best_path->partColsUpdated,
                            best_path->resultRelations,
+                           best_path->mergeTargetRelation,
                            subplans,
                            best_path->withCheckOptionLists,
                            best_path->returningLists,
                            best_path->rowMarks,
                            best_path->onconflict,
+                           best_path->mergeSourceTargetList,
+                           best_path->mergeActionList,
                            best_path->epqParam);
 
    copy_generic_path_info(&plan->plan, &best_path->path);
                 CmdType operation, bool canSetTag,
                 Index nominalRelation, List *partitioned_rels,
                 bool partColsUpdated,
-                List *resultRelations, List *subplans,
+                List *resultRelations,
+                Index mergeTargetRelation,
+                List *subplans,
                 List *withCheckOptionLists, List *returningLists,
-                List *rowMarks, OnConflictExpr *onconflict, int epqParam)
+                List *rowMarks, OnConflictExpr *onconflict,
+                List *mergeSourceTargetList,
+                List *mergeActionList, int epqParam)
 {
    ModifyTable *node = makeNode(ModifyTable);
    List       *fdw_private_list;
    node->partitioned_rels = partitioned_rels;
    node->partColsUpdated = partColsUpdated;
    node->resultRelations = resultRelations;
+   node->mergeTargetRelation = mergeTargetRelation;
    node->resultRelIndex = -1;  /* will be set correctly in setrefs.c */
    node->rootResultRelIndex = -1;  /* will be set correctly in setrefs.c */
    node->plans = subplans;
    node->withCheckOptionLists = withCheckOptionLists;
    node->returningLists = returningLists;
    node->rowMarks = rowMarks;
+   node->mergeSourceTargetList = mergeSourceTargetList;
+   node->mergeActionList = mergeActionList;
    node->epqParam = epqParam;
 
    /*
 
        /* exclRelTlist contains only Vars, so no preprocessing needed */
    }
 
+   foreach(l, parse->mergeActionList)
+   {
+       MergeAction *action = (MergeAction *) lfirst(l);
+
+       action->targetList = (List *)
+           preprocess_expression(root,
+                                 (Node *) action->targetList,
+                                 EXPRKIND_TARGET);
+       action->qual =
+           preprocess_expression(root,
+                                 (Node *) action->qual,
+                                 EXPRKIND_QUAL);
+   }
+
+   parse->mergeSourceTargetList = (List *)
+       preprocess_expression(root, (Node *) parse->mergeSourceTargetList,
+                             EXPRKIND_TARGET);
+
    root->append_rel_list = (List *)
        preprocess_expression(root, (Node *) root->append_rel_list,
                              EXPRKIND_APPINFO);
                                     subroot->parse->returningList);
 
        Assert(!parse->onConflict);
+       Assert(parse->mergeActionList == NIL);
    }
 
    /* Result path must go into outer query's FINAL upperrel */
                                     partitioned_rels,
                                     partColsUpdated,
                                     resultRelations,
+                                    0,
                                     subpaths,
                                     subroots,
                                     withCheckOptionLists,
                                     returningLists,
                                     rowMarks,
                                     NULL,
+                                    NULL,
+                                    NULL,
                                     SS_assign_special_param(root)));
 }
 
        }
 
        /*
-        * If this is an INSERT/UPDATE/DELETE, and we're not being called from
-        * inheritance_planner, add the ModifyTable node.
+        * If this is an INSERT/UPDATE/DELETE/MERGE, and we're not being
+        * called from inheritance_planner, add the ModifyTable node.
         */
        if (parse->commandType != CMD_SELECT && !inheritance_update)
        {
                                        NIL,
                                        false,
                                        list_make1_int(parse->resultRelation),
+                                       parse->mergeTarget_relation,
                                        list_make1(path),
                                        list_make1(root),
                                        withCheckOptionLists,
                                        returningLists,
                                        rowMarks,
                                        parse->onConflict,
+                                       parse->mergeSourceTargetList,
+                                       parse->mergeActionList,
                                        SS_assign_special_param(root));
        }
 
 
                        fix_scan_list(root, splan->exclRelTlist, rtoffset);
                }
 
+               /*
+                * The MERGE produces the target rows by performing a right
+                * join between the target relation and the source relation
+                * (which could be a plain relation or a subquery). The INSERT
+                * and UPDATE actions of the MERGE requires access to the
+                * columns from the source relation. We arrange things so that
+                * the source relation attributes are available as INNER_VAR
+                * and the target relation attributes are available from the
+                * scan tuple.
+                */
+               if (splan->mergeActionList != NIL)
+               {
+                   /*
+                    * mergeSourceTargetList is already setup correctly to
+                    * include all Vars coming from the source relation. So we
+                    * fix the targetList of individual action nodes by
+                    * ensuring that the source relation Vars are referenced
+                    * as INNER_VAR. Note that for this to work correctly,
+                    * during execution, the ecxt_innertuple must be set to
+                    * the tuple obtained from the source relation.
+                    *
+                    * We leave the Vars from the result relation (i.e. the
+                    * target relation) unchanged i.e. those Vars would be
+                    * picked from the scan slot. So during execution, we must
+                    * ensure that ecxt_scantuple is setup correctly to refer
+                    * to the tuple from the target relation.
+                    */
+
+                   indexed_tlist *itlist;
+
+                   itlist = build_tlist_index(splan->mergeSourceTargetList);
+
+                   splan->mergeTargetRelation += rtoffset;
+
+                   foreach(l, splan->mergeActionList)
+                   {
+                       MergeAction *action = (MergeAction *) lfirst(l);
+
+                       /* Fix targetList of each action. */
+                       action->targetList = fix_join_expr(root,
+                               action->targetList,
+                               NULL, itlist,
+                               linitial_int(splan->resultRelations),
+                               rtoffset);
+
+                       /* Fix quals too. */
+                       action->qual = (Node *) fix_join_expr(root,
+                               (List *) action->qual,
+                               NULL, itlist,
+                               linitial_int(splan->resultRelations),
+                               rtoffset);
+                   }
+               }
+
                splan->nominalRelation += rtoffset;
                splan->exclRelRTI += rtoffset;
 
 
        tlist = expand_targetlist(tlist, command_type,
                                  result_relation, target_relation);
 
+   if (command_type == CMD_MERGE)
+   {
+       ListCell   *l;
+
+       /*
+        * For MERGE, add any junk column(s) needed to allow the executor to
+        * identify the rows to be updated or deleted, with different
+        * handling for partitioned tables.
+        */
+       rewriteTargetListMerge(parse, target_relation);
+
+       /*
+        * For MERGE command, handle targetlist of each MergeAction separately.
+        * Give the same treatment to MergeAction->targetList as we would have
+        * given to a regular INSERT/UPDATE/DELETE.
+        */
+       foreach(l, parse->mergeActionList)
+       {
+           MergeAction *action = (MergeAction *) lfirst(l);
+
+           switch (action->commandType)
+           {
+               case CMD_INSERT:
+               case CMD_UPDATE:
+                   action->targetList = expand_targetlist(action->targetList,
+                                                          action->commandType,
+                                                          result_relation,
+                                                          target_relation);
+                   break;
+               case CMD_DELETE:
+                   break;
+               case CMD_NOTHING:
+                   break;
+               default:
+                   elog(ERROR, "unknown action in MERGE WHEN clause");
+
+           }
+       }
+   }
+
    /*
     * Add necessary junk columns for rowmarked rels.  These values are needed
     * for locking of rels selected FOR UPDATE/SHARE, and to do EvalPlanQual
                                                      true /* byval */ );
                    }
                    break;
+               case CMD_MERGE:
                case CMD_UPDATE:
                    if (!att_tup->attisdropped)
                    {
 
  * 'rowMarks' is a list of PlanRowMarks (non-locking only)
  * 'onconflict' is the ON CONFLICT clause, or NULL
  * 'epqParam' is the ID of Param for EvalPlanQual re-eval
+ * 'mergeActionList' is a list of MERGE actions
  */
 ModifyTablePath *
 create_modifytable_path(PlannerInfo *root, RelOptInfo *rel,
                        CmdType operation, bool canSetTag,
                        Index nominalRelation, List *partitioned_rels,
                        bool partColsUpdated,
-                       List *resultRelations, List *subpaths,
+                       List *resultRelations,
+                       Index mergeTargetRelation,
+                       List *subpaths,
                        List *subroots,
                        List *withCheckOptionLists, List *returningLists,
                        List *rowMarks, OnConflictExpr *onconflict,
-                       int epqParam)
+                       List *mergeSourceTargetList,
+                       List *mergeActionList, int epqParam)
 {
    ModifyTablePath *pathnode = makeNode(ModifyTablePath);
    double      total_size;
    pathnode->partitioned_rels = list_copy(partitioned_rels);
    pathnode->partColsUpdated = partColsUpdated;
    pathnode->resultRelations = resultRelations;
+   pathnode->mergeTargetRelation = mergeTargetRelation;
    pathnode->subpaths = subpaths;
    pathnode->subroots = subroots;
    pathnode->withCheckOptionLists = withCheckOptionLists;
    pathnode->rowMarks = rowMarks;
    pathnode->onconflict = onconflict;
    pathnode->epqParam = epqParam;
+   pathnode->mergeSourceTargetList = mergeSourceTargetList;
+   pathnode->mergeActionList = mergeActionList;
 
    return pathnode;
 }
 
                 trigDesc->trig_delete_before_row))
                result = true;
            break;
+           /* There is no separate event for MERGE, only INSERT/UPDATE/DELETE */
+       case CMD_MERGE:
+           result = false;
+           break;
        default:
            elog(ERROR, "unrecognized CmdType: %d", (int) event);
            break;
 
 
 OBJS= analyze.o gram.o scan.o parser.o \
       parse_agg.o parse_clause.o parse_coerce.o parse_collate.o parse_cte.o \
-      parse_enr.o parse_expr.o parse_func.o parse_node.o parse_oper.o \
+      parse_enr.o parse_expr.o parse_func.o parse_merge.o parse_node.o parse_oper.o \
       parse_param.o parse_relation.o parse_target.o parse_type.o \
       parse_utilcmd.o scansup.o
 
 
 #include "parser/parse_cte.h"
 #include "parser/parse_expr.h"
 #include "parser/parse_func.h"
+#include "parser/parse_merge.h"
 #include "parser/parse_oper.h"
 #include "parser/parse_param.h"
 #include "parser/parse_relation.h"
 static Query *transformOptionalSelectInto(ParseState *pstate, Node *parseTree);
 static Query *transformDeleteStmt(ParseState *pstate, DeleteStmt *stmt);
 static Query *transformInsertStmt(ParseState *pstate, InsertStmt *stmt);
-static List *transformInsertRow(ParseState *pstate, List *exprlist,
-                  List *stmtcols, List *icolumns, List *attrnos,
-                  bool strip_indirection);
 static OnConflictExpr *transformOnConflictClause(ParseState *pstate,
                          OnConflictClause *onConflictClause);
 static int count_rowexpr_columns(ParseState *pstate, Node *expr);
                           Node *larg, List *nrtargetlist);
 static Query *transformUpdateStmt(ParseState *pstate, UpdateStmt *stmt);
 static List *transformReturningList(ParseState *pstate, List *returningList);
-static List *transformUpdateTargetList(ParseState *pstate,
-                         List *targetList);
 static Query *transformDeclareCursorStmt(ParseState *pstate,
                           DeclareCursorStmt *stmt);
 static Query *transformExplainStmt(ParseState *pstate,
        case T_InsertStmt:
        case T_UpdateStmt:
        case T_DeleteStmt:
+       case T_MergeStmt:
            (void) test_raw_expression_coverage(parseTree, NULL);
            break;
        default:
            result = transformUpdateStmt(pstate, (UpdateStmt *) parseTree);
            break;
 
+       case T_MergeStmt:
+           result = transformMergeStmt(pstate, (MergeStmt *) parseTree);
+           break;
+
        case T_SelectStmt:
            {
                SelectStmt *n = (SelectStmt *) parseTree;
        case T_InsertStmt:
        case T_DeleteStmt:
        case T_UpdateStmt:
+       case T_MergeStmt:
        case T_SelectStmt:
            result = true;
            break;
  * attrnos: integer column numbers (must be same length as icolumns)
  * strip_indirection: if true, remove any field/array assignment nodes
  */
-static List *
+List *
 transformInsertRow(ParseState *pstate, List *exprlist,
                   List *stmtcols, List *icolumns, List *attrnos,
                   bool strip_indirection)
 
 /*
  * transformUpdateTargetList -
- * handle SET clause in UPDATE/INSERT ... ON CONFLICT UPDATE
+ * handle SET clause in UPDATE/MERGE/INSERT ... ON CONFLICT UPDATE
  */
-static List *
+List *
 transformUpdateTargetList(ParseState *pstate, List *origTlist)
 {
    List       *tlist = NIL;
 
        CreateMatViewStmt RefreshMatViewStmt CreateAmStmt
        CreatePublicationStmt AlterPublicationStmt
        CreateSubscriptionStmt AlterSubscriptionStmt DropSubscriptionStmt
+       MergeStmt
 
 %type <node>   select_no_parens select_with_parens select_clause
                simple_select values_clause
 %type <list>       hash_partbound partbound_datum_list range_datum_list
 %type <defelt>     hash_partbound_elem
 
+%type <node>   merge_when_clause opt_and_condition
+%type <list>   merge_when_list
+%type <node>   merge_update merge_delete merge_insert
+
 /*
  * Non-keyword token types.  These are hard-wired into the "flex" lexer.
  * They must be listed first so that their numeric codes do not depend on
    LEADING LEAKPROOF LEAST LEFT LEVEL LIKE LIMIT LISTEN LOAD LOCAL
    LOCALTIME LOCALTIMESTAMP LOCATION LOCK_P LOCKED LOGGED
 
-   MAPPING MATCH MATERIALIZED MAXVALUE METHOD MINUTE_P MINVALUE MODE MONTH_P MOVE
+   MAPPING MATCH MATCHED MATERIALIZED MAXVALUE MERGE METHOD
+   MINUTE_P MINVALUE MODE MONTH_P MOVE
 
    NAME_P NAMES NATIONAL NATURAL NCHAR NEW NEXT NO NONE
    NOT NOTHING NOTIFY NOTNULL NOWAIT NULL_P NULLIF
            | RefreshMatViewStmt
            | LoadStmt
            | LockStmt
+           | MergeStmt
            | NotifyStmt
            | PrepareStmt
            | ReassignOwnedStmt
            | InsertStmt
            | UpdateStmt
            | DeleteStmt
+           | MergeStmt
            | DeclareCursorStmt
            | CreateAsStmt
            | CreateMatViewStmt
            | InsertStmt
            | UpdateStmt
            | DeleteStmt                    /* by default all are $$=$1 */
+           | MergeStmt
        ;
 
 /*****************************************************************************
        ;
 
 
+/*****************************************************************************
+ *
+ *     QUERY:
+ *             MERGE STATEMENTS
+ *
+ *****************************************************************************/
+
+MergeStmt:
+           MERGE INTO relation_expr_opt_alias
+           USING table_ref
+           ON a_expr
+           merge_when_list
+               {
+                   MergeStmt *m = makeNode(MergeStmt);
+
+                   m->relation = $3;
+                   m->source_relation = $5;
+                   m->join_condition = $7;
+                   m->mergeActionList = $8;
+
+                   $$ = (Node *)m;
+               }
+           ;
+
+
+merge_when_list:
+           merge_when_clause                       { $$ = list_make1($1); }
+           | merge_when_list merge_when_clause     { $$ = lappend($1,$2); }
+           ;
+
+merge_when_clause:
+           WHEN MATCHED opt_and_condition THEN merge_update
+               {
+                   MergeAction *m = makeNode(MergeAction);
+
+                   m->matched = true;
+                   m->commandType = CMD_UPDATE;
+                   m->condition = $3;
+                   m->stmt = $5;
+
+                   $$ = (Node *)m;
+               }
+           | WHEN MATCHED opt_and_condition THEN merge_delete
+               {
+                   MergeAction *m = makeNode(MergeAction);
+
+                   m->matched = true;
+                   m->commandType = CMD_DELETE;
+                   m->condition = $3;
+                   m->stmt = $5;
+
+                   $$ = (Node *)m;
+               }
+           | WHEN NOT MATCHED opt_and_condition THEN merge_insert
+               {
+                   MergeAction *m = makeNode(MergeAction);
+
+                   m->matched = false;
+                   m->commandType = CMD_INSERT;
+                   m->condition = $4;
+                   m->stmt = $6;
+
+                   $$ = (Node *)m;
+               }
+           | WHEN NOT MATCHED opt_and_condition THEN DO NOTHING
+               {
+                   MergeAction *m = makeNode(MergeAction);
+
+                   m->matched = false;
+                   m->commandType = CMD_NOTHING;
+                   m->condition = $4;
+                   m->stmt = NULL;
+
+                   $$ = (Node *)m;
+               }
+           ;
+
+opt_and_condition:
+           AND a_expr              { $$ = $2; }
+           |                       { $$ = NULL; }
+           ;
+
+merge_delete:
+           DELETE_P
+               {
+                   DeleteStmt *n = makeNode(DeleteStmt);
+                   $$ = (Node *)n;
+               }
+           ;
+
+merge_update:
+           UPDATE SET set_clause_list
+               {
+                   UpdateStmt *n = makeNode(UpdateStmt);
+                   n->targetList = $3;
+
+                   $$ = (Node *)n;
+               }
+           ;
+
+merge_insert:
+           INSERT values_clause
+               {
+                   InsertStmt *n = makeNode(InsertStmt);
+                   n->cols = NIL;
+                   n->selectStmt = $2;
+
+                   $$ = (Node *)n;
+               }
+           | INSERT OVERRIDING override_kind VALUE_P values_clause
+               {
+                   InsertStmt *n = makeNode(InsertStmt);
+                   n->cols = NIL;
+                   n->override = $3;
+                   n->selectStmt = $5;
+
+                   $$ = (Node *)n;
+               }
+           | INSERT '(' insert_column_list ')' values_clause
+               {
+                   InsertStmt *n = makeNode(InsertStmt);
+                   n->cols = $3;
+                   n->selectStmt = $5;
+
+                   $$ = (Node *)n;
+               }
+           | INSERT '(' insert_column_list ')' OVERRIDING override_kind VALUE_P values_clause
+               {
+                   InsertStmt *n = makeNode(InsertStmt);
+                   n->cols = $3;
+                   n->override = $6;
+                   n->selectStmt = $8;
+
+                   $$ = (Node *)n;
+               }
+           | INSERT DEFAULT VALUES
+               {
+                   InsertStmt *n = makeNode(InsertStmt);
+                   n->cols = NIL;
+                   n->selectStmt = NULL;
+
+                   $$ = (Node *)n;
+               }
+           ;
+
 /*****************************************************************************
  *
  *     QUERY:
            | LOGGED
            | MAPPING
            | MATCH
+           | MATCHED
            | MATERIALIZED
            | MAXVALUE
+           | MERGE
            | METHOD
            | MINUTE_P
            | MINVALUE
 
        case EXPR_KIND_VALUES_SINGLE:
            errkind = true;
            break;
+       case EXPR_KIND_MERGE_WHEN_AND:
+           if (isAgg)
+               err = _("aggregate functions are not allowed in WHEN AND conditions");
+           else
+               err = _("grouping operations are not allowed in WHEN AND conditions");
+
+           break;
        case EXPR_KIND_CHECK_CONSTRAINT:
        case EXPR_KIND_DOMAIN_CHECK:
            if (isAgg)
        case EXPR_KIND_VALUES_SINGLE:
            errkind = true;
            break;
+       case EXPR_KIND_MERGE_WHEN_AND:
+           err = _("window functions are not allowed in WHEN AND conditions");
+           break;
        case EXPR_KIND_CHECK_CONSTRAINT:
        case EXPR_KIND_DOMAIN_CHECK:
            err = _("window functions are not allowed in check constraints");
 
                        RangeTableFunc *t);
 static TableSampleClause *transformRangeTableSample(ParseState *pstate,
                          RangeTableSample *rts);
-static Node *transformFromClauseItem(ParseState *pstate, Node *n,
-                       RangeTblEntry **top_rte, int *top_rti,
-                       List **namespace);
 static Node *buildMergedJoinVar(ParseState *pstate, JoinType jointype,
                   Var *l_colvar, Var *r_colvar);
 static ParseNamespaceItem *makeNamespaceItem(RangeTblEntry *rte,
        n = transformFromClauseItem(pstate, n,
                                    &rte,
                                    &rtindex,
+                                   NULL, NULL,
                                    &namespace);
 
        checkNameSpaceConflicts(pstate, pstate->p_namespace, namespace);
  *
  * *top_rti: receives the rangetable index of top_rte.  (Ditto.)
  *
+ * *right_rte: receives the RTE corresponding to the right side of the
+ * jointree. Only MERGE really needs to know about this and only MERGE passes a
+ * non-NULL pointer.
+ *
+ * *right_rti: receives the rangetable index of the right_rte.
+ *
  * *namespace: receives a List of ParseNamespaceItems for the RTEs exposed
  * as table/column names by this item.  (The lateral_only flags in these items
  * are indeterminate and should be explicitly set by the caller before use.)
  */
-static Node *
+Node *
 transformFromClauseItem(ParseState *pstate, Node *n,
                        RangeTblEntry **top_rte, int *top_rti,
+                       RangeTblEntry **right_rte, int *right_rti,
                        List **namespace)
 {
    if (IsA(n, RangeVar))
 
        /* Recursively transform the contained relation */
        rel = transformFromClauseItem(pstate, rts->relation,
-                                     top_rte, top_rti, namespace);
+                                     top_rte, top_rti, NULL, NULL, namespace);
        /* Currently, grammar could only return a RangeVar as contained rel */
        rtr = castNode(RangeTblRef, rel);
        rte = rt_fetch(rtr->rtindex, pstate->p_rtable);
        List       *l_namespace,
                   *r_namespace,
                   *my_namespace,
+                  *save_namespace,
                   *l_colnames,
                   *r_colnames,
                   *res_colnames,
        j->larg = transformFromClauseItem(pstate, j->larg,
                                          &l_rte,
                                          &l_rtindex,
+                                         NULL, NULL,
                                          &l_namespace);
 
        /*
        sv_namespace_length = list_length(pstate->p_namespace);
        pstate->p_namespace = list_concat(pstate->p_namespace, l_namespace);
 
+       /*
+        * If we are running MERGE, don't make the other RTEs visible while
+        * parsing the source relation. It mustn't see them.
+        *
+        * Currently, only MERGE passes non-NULL value for right_rte, so we
+        * can safely deduce if we're running MERGE or not by just looking at
+        * the right_rte. If that ever changes, we should look at other means
+        * to find that.
+        */
+       if (right_rte)
+       {
+           save_namespace = pstate->p_namespace;
+           pstate->p_namespace = NIL;
+       }
+
        /* And now we can process the RHS */
        j->rarg = transformFromClauseItem(pstate, j->rarg,
                                          &r_rte,
                                          &r_rtindex,
+                                         NULL, NULL,
                                          &r_namespace);
 
+       /*
+        * And now restore the namespace again so that join-quals can see it.
+        */
+       if (right_rte)
+           pstate->p_namespace = save_namespace;
+
        /* Remove the left-side RTEs from the namespace list again */
        pstate->p_namespace = list_truncate(pstate->p_namespace,
                                            sv_namespace_length);
        expandRTE(r_rte, r_rtindex, 0, -1, false,
                  &r_colnames, &r_colvars);
 
+       if (right_rte)
+           *right_rte = r_rte;
+
+       if (right_rti)
+           *right_rti = r_rtindex;
+
        /*
         * Natural join does not explicitly specify columns; must generate
         * columns to join. Need to run through the list of columns from each
 
        case T_FromExpr:
        case T_OnConflictExpr:
        case T_SortGroupClause:
+       case T_MergeAction:
            (void) expression_tree_walker(node,
                                          assign_collations_walker,
                                          (void *) &loccontext);
 
        case EXPR_KIND_RETURNING:
        case EXPR_KIND_VALUES:
        case EXPR_KIND_VALUES_SINGLE:
+       case EXPR_KIND_MERGE_WHEN_AND:
            /* okay */
            break;
        case EXPR_KIND_CHECK_CONSTRAINT:
            return "PARTITION BY";
        case EXPR_KIND_CALL_ARGUMENT:
            return "CALL";
+       case EXPR_KIND_MERGE_WHEN_AND:
+           return "MERGE WHEN AND";
 
            /*
             * There is intentionally no default: case here, so that the
 
            /* okay, since we process this like a SELECT tlist */
            pstate->p_hasTargetSRFs = true;
            break;
+       case EXPR_KIND_MERGE_WHEN_AND:
+           err = _("set-returning functions are not allowed in WHEN AND conditions");
+           break;
        case EXPR_KIND_CHECK_CONSTRAINT:
        case EXPR_KIND_DOMAIN_CHECK:
            err = _("set-returning functions are not allowed in check constraints");
 
                            colname),
                     parser_errposition(pstate, location)));
 
+       /* In MERGE WHEN AND condition, no system column is allowed except tableOid or OID */
+       if (pstate->p_expr_kind == EXPR_KIND_MERGE_WHEN_AND &&
+           attnum < InvalidAttrNumber &&
+           !(attnum == TableOidAttributeNumber || attnum == ObjectIdAttributeNumber))
+           ereport(ERROR,
+                   (errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
+                    errmsg("system column \"%s\" reference in WHEN AND condition is invalid",
+                           colname),
+                    parser_errposition(pstate, location)));
+
        if (attnum != InvalidAttrNumber)
        {
            /* now check to see if column actually is defined */
 
    }
 }
 
+void
+rewriteTargetListMerge(Query *parsetree, Relation target_relation)
+{
+   Var        *var = NULL;
+   const char *attrname;
+   TargetEntry *tle;
+
+   Assert(target_relation->rd_rel->relkind == RELKIND_RELATION ||
+          target_relation->rd_rel->relkind == RELKIND_MATVIEW ||
+          target_relation->rd_rel->relkind == RELKIND_PARTITIONED_TABLE);
+
+   /*
+    * Emit CTID so that executor can find the row to update or delete.
+    */
+   var = makeVar(parsetree->mergeTarget_relation,
+                 SelfItemPointerAttributeNumber,
+                 TIDOID,
+                 -1,
+                 InvalidOid,
+                 0);
+
+   attrname = "ctid";
+   tle = makeTargetEntry((Expr *) var,
+                         list_length(parsetree->targetList) + 1,
+                         pstrdup(attrname),
+                         true);
+
+   parsetree->targetList = lappend(parsetree->targetList, tle);
+
+   /*
+    * If we are dealing with partitioned table, then emit TABLEOID so that
+    * executor can find the partition the row belongs to.
+    */
+   if (target_relation->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
+   {
+       var = makeVar(parsetree->mergeTarget_relation,
+               TableOidAttributeNumber,
+               OIDOID,
+               -1,
+               InvalidOid,
+               0);
+
+       attrname = "tableoid";
+       tle = makeTargetEntry((Expr *) var,
+               list_length(parsetree->targetList) + 1,
+               pstrdup(attrname),
+               true);
+
+       parsetree->targetList = lappend(parsetree->targetList, tle);
+   }
+}
 
 /*
  * matchLocks -
        }
        else if (event == CMD_UPDATE)
        {
+           Assert(parsetree->override == OVERRIDING_NOT_SET);
            parsetree->targetList =
                rewriteTargetListIU(parsetree->targetList,
                                    parsetree->commandType,
                                    rt_entry_relation,
                                    parsetree->resultRelation, NULL);
        }
+       else if (event == CMD_MERGE)
+       {
+           Assert(parsetree->override == OVERRIDING_NOT_SET);
+
+           /*
+            * Rewrite each action targetlist separately
+            */
+           foreach(lc1, parsetree->mergeActionList)
+           {
+               MergeAction *action = (MergeAction *) lfirst(lc1);
+
+               switch (action->commandType)
+               {
+                   case CMD_NOTHING:
+                   case CMD_DELETE:    /* Nothing to do here */
+                       break;
+                   case CMD_UPDATE:
+                       action->targetList =
+                           rewriteTargetListIU(action->targetList,
+                                               action->commandType,
+                                               parsetree->override,
+                                               rt_entry_relation,
+                                               parsetree->resultRelation,
+                                               NULL);
+                       break;
+                   case CMD_INSERT:
+                       {
+                           InsertStmt *istmt = (InsertStmt *) action->stmt;
+
+                           action->targetList =
+                               rewriteTargetListIU(action->targetList,
+                                                   action->commandType,
+                                                   istmt->override,
+                                                   rt_entry_relation,
+                                                   parsetree->resultRelation,
+                                                   NULL);
+                       }
+                       break;
+                   default:
+                       elog(ERROR, "unrecognized commandType: %d", action->commandType);
+                       break;
+               }
+           }
+       }
        else if (event == CMD_DELETE)
        {
            /* Nothing to do here */
        locks = matchLocks(event, rt_entry_relation->rd_rules,
                           result_relation, parsetree, &hasUpdate);
 
-       product_queries = fireRules(parsetree,
-                                   result_relation,
-                                   event,
-                                   locks,
-                                   &instead,
-                                   &returning,
-                                   &qual_product);
+       /*
+        * XXX MERGE doesn't support write rules because they would violate
+        * the SQL Standard spec and would be unclear how they should work.
+        */
+       if (event == CMD_MERGE)
+           product_queries = NIL;
+       else
+           product_queries = fireRules(parsetree,
+                                       result_relation,
+                                       event,
+                                       locks,
+                                       &instead,
+                                       &returning,
+                                       &qual_product);
 
        /*
         * If there were no INSTEAD rules, and the target relation is a view
 
        }
    }
 
+   /*
+    * FOR MERGE, we fetch policies for UPDATE, DELETE and INSERT (and ALL)
+    * and set them up so that we can enforce the appropriate policy depending
+    * on the final action we take.
+    *
+    * We don't fetch the SELECT policies since they are correctly applied to
+    * the root->mergeTarget_relation. The target rows are selected after
+    * joining the mergeTarget_relation and the source relation and hence it's
+    * enough to apply SELECT policies to the mergeTarget_relation.
+    *
+    * We don't push the UPDATE/DELETE USING quals to the RTE because we don't
+    * really want to apply them while scanning the relation since we don't
+    * know whether we will be doing a UPDATE or a DELETE at the end. We apply
+    * the respective policy once we decide the final action on the target
+    * tuple.
+    *
+    * XXX We are setting up USING quals as WITH CHECK. If RLS prohibits
+    * UPDATE/DELETE on the target row, we shall throw an error instead of
+    * silently ignoring the row. This is different than how normal
+    * UPDATE/DELETE works and more in line with INSERT ON CONFLICT DO UPDATE
+    * handling.
+    */
+   if (commandType == CMD_MERGE)
+   {
+       List       *merge_permissive_policies;
+       List       *merge_restrictive_policies;
+
+       /*
+        * Fetch the UPDATE policies and set them up to execute on the
+        * existing target row before doing UPDATE.
+        */
+       get_policies_for_relation(rel, CMD_UPDATE, user_id,
+                                 &merge_permissive_policies,
+                                 &merge_restrictive_policies);
+
+       /*
+        * WCO_RLS_MERGE_UPDATE_CHECK is used to check UPDATE USING quals on
+        * the existing target row.
+        */
+       add_with_check_options(rel, rt_index,
+                              WCO_RLS_MERGE_UPDATE_CHECK,
+                              merge_permissive_policies,
+                              merge_restrictive_policies,
+                              withCheckOptions,
+                              hasSubLinks,
+                              true);
+
+       /*
+        * Same with DELETE policies.
+        */
+       get_policies_for_relation(rel, CMD_DELETE, user_id,
+                                 &merge_permissive_policies,
+                                 &merge_restrictive_policies);
+
+       add_with_check_options(rel, rt_index,
+                              WCO_RLS_MERGE_DELETE_CHECK,
+                              merge_permissive_policies,
+                              merge_restrictive_policies,
+                              withCheckOptions,
+                              hasSubLinks,
+                              true);
+
+       /*
+        * No special handling is required for INSERT policies. They will be
+        * checked and enforced during ExecInsert(). But we must add them to
+        * withCheckOptions.
+        */
+       get_policies_for_relation(rel, CMD_INSERT, user_id,
+                                 &merge_permissive_policies,
+                                 &merge_restrictive_policies);
+
+       add_with_check_options(rel, rt_index,
+                              WCO_RLS_INSERT_CHECK,
+                              merge_permissive_policies,
+                              merge_restrictive_policies,
+                              withCheckOptions,
+                              hasSubLinks,
+                              false);
+
+       /* Enforce the WITH CHECK clauses of the UPDATE policies */
+       add_with_check_options(rel, rt_index,
+                              WCO_RLS_UPDATE_CHECK,
+                              merge_permissive_policies,
+                              merge_restrictive_policies,
+                              withCheckOptions,
+                              hasSubLinks,
+                              false);
+   }
+
    heap_close(rel, NoLock);
 
    /*
                    if (policy->polcmd == ACL_DELETE_CHR)
                        cmd_matches = true;
                    break;
+               case CMD_MERGE:
+
+                   /*
+                    * We do not support a separate policy for MERGE command.
+                    * Instead it derives from the policies defined for other
+                    * commands.
+                    */
+                   break;
                default:
                    elog(ERROR, "unrecognized policy command type %d",
                         (int) cmd);
 
                         "DELETE " UINT64_FORMAT,
                         queryDesc->estate->es_processed);
                break;
+           case CMD_MERGE:
+               snprintf(completionTag, COMPLETION_TAG_BUFSIZE,
+                        "MERGE " UINT64_FORMAT,
+                        queryDesc->estate->es_processed);
+               break;
            default:
                strcpy(completionTag, "???");
                break;
 
        case CMD_UPDATE:
        case CMD_INSERT:
        case CMD_DELETE:
+       case CMD_MERGE:
            return false;
        case CMD_UTILITY:
            /* For now, treat all utility commands as read/write */
        case CMD_SELECT:
            /* returns tuples */
            return true;
+       case CMD_MERGE:
+           return false;
        case CMD_INSERT:
        case CMD_UPDATE:
        case CMD_DELETE:
            tag = "UPDATE";
            break;
 
+       case T_MergeStmt:
+           tag = "MERGE";
+           break;
+
        case T_SelectStmt:
            tag = "SELECT";
            break;
                    case CMD_DELETE:
                        tag = "DELETE";
                        break;
+                   case CMD_MERGE:
+                       tag = "MERGE";
+                       break;
                    case CMD_UTILITY:
                        tag = CreateCommandTag(stmt->utilityStmt);
                        break;
                    case CMD_DELETE:
                        tag = "DELETE";
                        break;
+                   case CMD_MERGE:
+                       tag = "MERGE";
+                       break;
                    case CMD_UTILITY:
                        tag = CreateCommandTag(stmt->utilityStmt);
                        break;
        case T_InsertStmt:
        case T_DeleteStmt:
        case T_UpdateStmt:
+       case T_MergeStmt:
            lev = LOGSTMT_MOD;
            break;
 
                    case CMD_UPDATE:
                    case CMD_INSERT:
                    case CMD_DELETE:
+                   case CMD_MERGE:
                        lev = LOGSTMT_MOD;
                        break;
 
                    case CMD_UPDATE:
                    case CMD_INSERT:
                    case CMD_DELETE:
+                   case CMD_MERGE:
                        lev = LOGSTMT_MOD;
                        break;
 
 
  * When heap_update, heap_delete, or heap_lock_tuple fail because the target
  * tuple is already outdated, they fill in this struct to provide information
  * to the caller about what happened.
+ *
+ * result is the result of HeapTupleSatisfiesUpdate, leading to the failure.
+ * It's set to HeapTupleMayBeUpdated when there is no failure.
+ *
  * ctid is the target's ctid link: it is the same as the target's TID if the
  * target was deleted, or the location of the replacement tuple if the target
  * was updated.
+ *
  * xmax is the outdating transaction's XID.  If the caller wants to visit the
  * replacement tuple, it must check that this matches before believing the
  * replacement is really a match.
+ *
  * cmax is the outdating command's CID, but only when the failure code is
  * HeapTupleSelfUpdated (i.e., something in the current transaction outdated
  * the tuple); otherwise cmax is zero.  (We make this restriction because
  * HeapTupleHeaderGetCmax doesn't work for tuples outdated in other
  * transactions.)
+ *
+ * lockmode is only relevant for callers of heap_update() and is the mode which
+ * the caller should use in case it needs to lock the updated tuple.
  */
 typedef struct HeapUpdateFailureData
 {
+   HTSU_Result result;
    ItemPointerData ctid;
    TransactionId xmax;
    CommandId   cmax;
+   LockTupleMode   lockmode;
 } HeapUpdateFailureData;
 
 
 extern HTSU_Result heap_update(Relation relation, ItemPointer otid,
            HeapTuple newtup,
            CommandId cid, Snapshot crosscheck, bool wait,
-           HeapUpdateFailureData *hufd, LockTupleMode *lockmode);
+           HeapUpdateFailureData *hufd);
 extern HTSU_Result heap_lock_tuple(Relation relation, HeapTuple tuple,
                CommandId cid, LockTupleMode mode, LockWaitPolicy wait_policy,
                bool follow_update,
 
                     EPQState *epqstate,
                     ResultRelInfo *relinfo,
                     ItemPointer tupleid,
-                    HeapTuple fdw_trigtuple);
+                    HeapTuple fdw_trigtuple,
+                    HeapUpdateFailureData *hufdp);
 extern void ExecARDeleteTriggers(EState *estate,
                     ResultRelInfo *relinfo,
                     ItemPointer tupleid,
                     ResultRelInfo *relinfo,
                     ItemPointer tupleid,
                     HeapTuple fdw_trigtuple,
-                    TupleTableSlot *slot);
+                    TupleTableSlot *slot,
+                    HeapUpdateFailureData *hufdp);
 extern void ExecARUpdateTriggers(EState *estate,
                     ResultRelInfo *relinfo,
                     ItemPointer tupleid,
 
                  PartitionDispatch *pd,
                  TupleTableSlot *slot,
                  EState *estate);
+extern int ExecFindPartitionByOid(PartitionTupleRouting *proute, Oid partoid);
 extern ResultRelInfo *ExecInitPartitionInfo(ModifyTableState *mtstate,
                    ResultRelInfo *resultRelInfo,
                    PartitionTupleRouting *proute,
 
    double      total;          /* Total total time (in seconds) */
    double      ntuples;        /* Total tuples produced */
    double      nloops;         /* # of run cycles for this node */
-   double      nfiltered1;     /* # tuples removed by scanqual or joinqual */
-   double      nfiltered2;     /* # tuples removed by "other" quals */
+   double      nfiltered1;     /* # tuples removed by scanqual or joinqual OR
+                                * # tuples inserted by MERGE */
+   double      nfiltered2;     /* # tuples removed by "other" quals OR
+                                * # tuples updated by MERGE */
+   double      nfiltered3;     /* # tuples deleted by MERGE */
    BufferUsage bufusage;       /* Total buffer usage */
 } Instrumentation;
 
 
 extern ModifyTableState *ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags);
 extern void ExecEndModifyTable(ModifyTableState *node);
 extern void ExecReScanModifyTable(ModifyTableState *node);
+extern TupleTableSlot *ExecPrepareTupleRouting(ModifyTableState *mtstate,
+                       EState *estate,
+                       struct PartitionTupleRouting *proute,
+                       ResultRelInfo *targetRelInfo,
+                       TupleTableSlot *slot);
+extern TupleTableSlot *ExecDelete(ModifyTableState *mtstate,
+          ItemPointer tupleid, HeapTuple oldtuple, TupleTableSlot *planSlot,
+          EPQState *epqstate, EState *estate, bool *tupleDeleted,
+          bool processReturning, HeapUpdateFailureData *hufdp,
+          MergeActionState *actionState, bool canSetTag);
+extern TupleTableSlot *ExecUpdate(ModifyTableState *mtstate,
+          ItemPointer tupleid, HeapTuple oldtuple, TupleTableSlot *slot,
+          TupleTableSlot *planSlot, EPQState *epqstate, EState *estate,
+          bool *tuple_updated, HeapUpdateFailureData *hufdp,
+          MergeActionState *actionState, bool canSetTag);
+extern TupleTableSlot *ExecInsert(ModifyTableState *mtstate,
+          TupleTableSlot *slot,
+          TupleTableSlot *planSlot,
+          EState *estate,
+          MergeActionState *actionState,
+          bool canSetTag);
 
 #endif                         /* NODEMODIFYTABLE_H */
 
 #define SPI_OK_REL_REGISTER        15
 #define SPI_OK_REL_UNREGISTER  16
 #define SPI_OK_TD_REGISTER     17
+#define SPI_OK_MERGE           18
 
 #define SPI_OPT_NONATOMIC      (1 << 0)
 
 
    AttrNumber *jf_cleanMap;
    TupleTableSlot *jf_resultSlot;
    AttrNumber  jf_junkAttNo;
+   AttrNumber  jf_otherJunkAttNo;
 } JunkFilter;
 
+typedef struct MergeState
+{
+   /* List of MERGE MATCHED action states */
+   List           *matchedActionStates;
+   /* List of MERGE NOT MATCHED action states */
+   List           *notMatchedActionStates;
+} MergeState;
+
 /*
  * OnConflictSetState
  *
 
    /* relation descriptor for root partitioned table */
    Relation    ri_PartitionRoot;
+
+   int         ri_PartitionLeafIndex;
+   /* for running MERGE on this result relation */
+   MergeState *ri_mergeState;
+
+   /*
+    * While executing MERGE, the target relation is processed twice; once
+    * as a target relation and once to run a join between the target and the
+    * source. We generate two different RTEs for these two purposes, one with
+    * rte->inh set to false and other with rte->inh set to true.
+    *
+    * Since the plan re-evaluated by EvalPlanQual uses the join RTE, we must
+    * install the updated tuple in the scan corresponding to that RTE. The
+    * following member tracks the index of the second RTE for EvalPlanQual
+    * purposes. ri_mergeTargetRTI is non-zero only when MERGE is in-progress.
+    * We use ri_mergeTargetRTI to run EvalPlanQual for MERGE and
+    * ri_RangeTableIndex elsewhere.
+    */
+   Index       ri_mergeTargetRTI;
 } ResultRelInfo;
 
+/*
+ * Get the Range table index for EvalPlanQual.
+ *
+ * We use the ri_mergeTargetRTI if set, otherwise use ri_RangeTableIndex.
+ * ri_mergeTargetRTI should really be ever set iff we're running MERGE.
+ */
+#define GetEPQRangeTableIndex(r) \
+   (((r)->ri_mergeTargetRTI > 0)  \
+    ? (r)->ri_mergeTargetRTI \
+    : (r)->ri_RangeTableIndex)
+
 /* ----------------
  *   EState information
  *
        if (((PlanState *)(node))->instrument) \
            ((PlanState *)(node))->instrument->nfiltered2 += (delta); \
    } while(0)
+#define InstrCountFiltered3(node, delta) \
+   do { \
+       if (((PlanState *)(node))->instrument) \
+           ((PlanState *)(node))->instrument->nfiltered3 += (delta); \
+   } while(0)
 
 /*
  * EPQState is state for executing an EvalPlanQual recheck on a candidate
    MemoryContext argcontext;   /* context for SRF arguments */
 } ProjectSetState;
 
+/* ----------------
+ *  MergeActionState information
+ * ----------------
+ */
+typedef struct MergeActionState
+{
+   NodeTag     type;
+   bool        matched;        /* true=MATCHED, false=NOT MATCHED */
+   ExprState  *whenqual;       /* WHEN AND conditions */
+   CmdType     commandType;    /* INSERT/UPDATE/DELETE/DO NOTHING */
+   ProjectionInfo *proj;       /* tuple projection info */
+   TupleDesc   tupDesc;        /* tuple descriptor for projection */
+} MergeActionState;
+
 /* ----------------
  *  ModifyTableState information
  * ----------------
 typedef struct ModifyTableState
 {
    PlanState   ps;             /* its first field is NodeTag */
-   CmdType     operation;      /* INSERT, UPDATE, or DELETE */
+   CmdType     operation;      /* INSERT, UPDATE, DELETE or MERGE */
    bool        canSetTag;      /* do we set the command tag/es_processed? */
    bool        mt_done;        /* are we done? */
    PlanState **mt_plans;       /* subplans (one per target rel) */
    List       *mt_excludedtlist;   /* the excluded pseudo relation's tlist  */
    TupleTableSlot *mt_conflproj;   /* CONFLICT ... SET ... projection target */
 
+   TupleTableSlot *mt_mergeproj;   /* MERGE action projection target */
+
    /* Tuple-routing support info */
    struct PartitionTupleRouting *mt_partition_tuple_routing;
 
 
    /* Per plan map for tuple conversion from child to root */
    TupleConversionMap **mt_per_subplan_tupconv_maps;
+
+   /* Flags showing which subcommands are present INS/UPD/DEL/DO NOTHING */
+   int         mt_merge_subcommands;
 } ModifyTableState;
 
 /* ----------------
 
    T_PlanState,
    T_ResultState,
    T_ProjectSetState,
+   T_MergeActionState,
    T_ModifyTableState,
    T_AppendState,
    T_MergeAppendState,
    T_InsertStmt,
    T_DeleteStmt,
    T_UpdateStmt,
+   T_MergeStmt,
+   T_MergeAction,
    T_SelectStmt,
    T_AlterTableStmt,
    T_AlterTableCmd,
    CMD_SELECT,                 /* select stmt */
    CMD_UPDATE,                 /* update stmt */
    CMD_INSERT,                 /* insert stmt */
-   CMD_DELETE,
+   CMD_DELETE,                 /* delete stmt */
+   CMD_MERGE,                  /* merge stmt */
    CMD_UTILITY,                /* cmds like create, destroy, copy, vacuum,
                                 * etc. */
    CMD_NOTHING                 /* dummy command for instead nothing rules
 
 typedef enum QuerySource
 {
    QSRC_ORIGINAL,              /* original parsetree (explicit query) */
-   QSRC_PARSER,                /* added by parse analysis (now unused) */
+   QSRC_PARSER,                /* added by parse analysis in MERGE */
    QSRC_INSTEAD_RULE,          /* added by unconditional INSTEAD rule */
    QSRC_QUAL_INSTEAD_RULE,     /* added by conditional INSTEAD rule */
    QSRC_NON_INSTEAD_RULE       /* added by non-INSTEAD rule */
 {
    NodeTag     type;
 
-   CmdType     commandType;    /* select|insert|update|delete|utility */
+   CmdType     commandType;    /* select|insert|update|delete|merge|utility */
 
    QuerySource querySource;    /* where did I come from? */
 
    Node       *utilityStmt;    /* non-null if commandType == CMD_UTILITY */
 
    int         resultRelation; /* rtable index of target relation for
-                                * INSERT/UPDATE/DELETE; 0 for SELECT */
+                                * INSERT/UPDATE/DELETE/MERGE; 0 for SELECT */
 
    bool        hasAggs;        /* has aggregates in tlist or havingQual */
    bool        hasWindowFuncs; /* has window functions in tlist */
    List       *withCheckOptions;   /* a list of WithCheckOption's, which are
                                     * only added during rewrite and therefore
                                     * are not written out as part of Query. */
+   int         mergeTarget_relation;
+   List       *mergeSourceTargetList;
+   List       *mergeActionList;    /* list of actions for MERGE (only) */
 
    /*
     * The following two fields identify the portion of the source text string
    WCO_VIEW_CHECK,             /* WCO on an auto-updatable view */
    WCO_RLS_INSERT_CHECK,       /* RLS INSERT WITH CHECK policy */
    WCO_RLS_UPDATE_CHECK,       /* RLS UPDATE WITH CHECK policy */
-   WCO_RLS_CONFLICT_CHECK      /* RLS ON CONFLICT DO UPDATE USING policy */
+   WCO_RLS_CONFLICT_CHECK,     /* RLS ON CONFLICT DO UPDATE USING policy */
+   WCO_RLS_MERGE_UPDATE_CHECK, /* RLS MERGE UPDATE USING policy */
+   WCO_RLS_MERGE_DELETE_CHECK  /* RLS MERGE DELETE USING policy */
 } WCOKind;
 
 typedef struct WithCheckOption
    WithClause *withClause;     /* WITH clause */
 } UpdateStmt;
 
+/* ----------------------
+ *     Merge Statement
+ * ----------------------
+ */
+typedef struct MergeStmt
+{
+   NodeTag     type;
+   RangeVar   *relation;           /* target relation to merge into */
+   Node       *source_relation;    /* source relation */
+   Node       *join_condition; /* join condition between source and target */
+   List       *mergeActionList;    /* list of MergeAction(s) */
+} MergeStmt;
+
+typedef struct MergeAction
+{
+   NodeTag     type;
+   bool        matched;        /* true=MATCHED, false=NOT MATCHED */
+   Node       *condition;      /* WHEN AND conditions (raw parser) */
+   Node       *qual;           /* transformed WHEN AND conditions */
+   CmdType     commandType;    /* INSERT/UPDATE/DELETE/DO NOTHING */
+   Node       *stmt;           /* T_UpdateStmt etc */
+   List       *targetList;     /* the target list (of ResTarget) */
+} MergeAction;
+
 /* ----------------------
  *     Select Statement
  *
 
 #include "lib/stringinfo.h"
 #include "nodes/bitmapset.h"
 #include "nodes/lockoptions.h"
+#include "nodes/parsenodes.h"
 #include "nodes/primnodes.h"
 
 
 {
    NodeTag     type;
 
-   CmdType     commandType;    /* select|insert|update|delete|utility */
+   CmdType     commandType;    /* select|insert|update|delete|merge|utility */
 
    uint64      queryId;        /* query identifier (copied from Query) */
 
 typedef struct ModifyTable
 {
    Plan        plan;
-   CmdType     operation;      /* INSERT, UPDATE, or DELETE */
+   CmdType     operation;      /* INSERT, UPDATE, DELETE or MERGE */
    bool        canSetTag;      /* do we set the command tag/es_processed? */
    Index       nominalRelation;    /* Parent RT index for use of EXPLAIN */
    /* RT indexes of non-leaf tables in a partition tree */
    List       *partitioned_rels;
    bool        partColsUpdated;    /* some part key in hierarchy updated */
    List       *resultRelations;    /* integer list of RT indexes */
+   Index       mergeTargetRelation;    /* RT index of the merge target */
    int         resultRelIndex; /* index of first resultRel in plan's list */
    int         rootResultRelIndex; /* index of the partitioned table root */
    List       *plans;          /* plan(s) producing source data */
    Node       *onConflictWhere;    /* WHERE for ON CONFLICT UPDATE */
    Index       exclRelRTI;     /* RTI of the EXCLUDED pseudo relation */
    List       *exclRelTlist;   /* tlist of the EXCLUDED pseudo relation */
+   List       *mergeSourceTargetList;
+   List       *mergeActionList;    /* actions for MERGE */
 } ModifyTable;
 
 /* ----------------
 
 } LockRowsPath;
 
 /*
- * ModifyTablePath represents performing INSERT/UPDATE/DELETE modifications
+ * ModifyTablePath represents performing INSERT/UPDATE/DELETE/MERGE
  *
  * We represent most things that will be in the ModifyTable plan node
  * literally, except we have child Path(s) not Plan(s).  But analysis of the
 typedef struct ModifyTablePath
 {
    Path        path;
-   CmdType     operation;      /* INSERT, UPDATE, or DELETE */
+   CmdType     operation;      /* INSERT, UPDATE, DELETE or MERGE */
    bool        canSetTag;      /* do we set the command tag/es_processed? */
    Index       nominalRelation;    /* Parent RT index for use of EXPLAIN */
    /* RT indexes of non-leaf tables in a partition tree */
    List       *partitioned_rels;
    bool        partColsUpdated;    /* some part key in hierarchy updated */
    List       *resultRelations;    /* integer list of RT indexes */
+   Index       mergeTargetRelation;/* RT index of merge target relation */
    List       *subpaths;       /* Path(s) producing source data */
    List       *subroots;       /* per-target-table PlannerInfos */
    List       *withCheckOptionLists;   /* per-target-table WCO lists */
    List       *rowMarks;       /* PlanRowMarks (non-locking only) */
    OnConflictExpr *onconflict; /* ON CONFLICT clause, or NULL */
    int         epqParam;       /* ID of Param for EvalPlanQual re-eval */
+   List       *mergeSourceTargetList;
+   List       *mergeActionList;    /* actions for MERGE */
 } ModifyTablePath;
 
 /*
 
                        CmdType operation, bool canSetTag,
                        Index nominalRelation, List *partitioned_rels,
                        bool partColsUpdated,
-                       List *resultRelations, List *subpaths,
+                       List *resultRelations,
+                       Index   mergeTargetRelation,
+                       List *subpaths,
                        List *subroots,
                        List *withCheckOptionLists, List *returningLists,
                        List *rowMarks, OnConflictExpr *onconflict,
-                       int epqParam);
+                       List *mergeSourceTargetList,
+                       List *mergeActionList, int epqParam);
 extern LimitPath *create_limit_path(PlannerInfo *root, RelOptInfo *rel,
                  Path *subpath,
                  Node *limitOffset, Node *limitCount,
 
                  bool locked_from_parent,
                  bool resolve_unknowns);
 
+extern List *transformInsertRow(ParseState *pstate, List *exprlist,
+                  List *stmtcols, List *icolumns, List *attrnos,
+                  bool strip_indirection);
+extern List *transformUpdateTargetList(ParseState *pstate,
+                         List *targetList);
 extern Query *transformTopLevelStmt(ParseState *pstate, RawStmt *parseTree);
 extern Query *transformStmt(ParseState *pstate, Node *parseTree);
 
 
 PG_KEYWORD("logged", LOGGED, UNRESERVED_KEYWORD)
 PG_KEYWORD("mapping", MAPPING, UNRESERVED_KEYWORD)
 PG_KEYWORD("match", MATCH, UNRESERVED_KEYWORD)
+PG_KEYWORD("matched", MATCHED, UNRESERVED_KEYWORD)
 PG_KEYWORD("materialized", MATERIALIZED, UNRESERVED_KEYWORD)
 PG_KEYWORD("maxvalue", MAXVALUE, UNRESERVED_KEYWORD)
+PG_KEYWORD("merge", MERGE, UNRESERVED_KEYWORD)
 PG_KEYWORD("method", METHOD, UNRESERVED_KEYWORD)
 PG_KEYWORD("minute", MINUTE_P, UNRESERVED_KEYWORD)
 PG_KEYWORD("minvalue", MINVALUE, UNRESERVED_KEYWORD)
 
 extern int setTargetTable(ParseState *pstate, RangeVar *relation,
               bool inh, bool alsoSource, AclMode requiredPerms);
 extern bool interpretOidsOption(List *defList, bool allowOids);
-
+extern Node *transformFromClauseItem(ParseState *pstate, Node *n,
+                       RangeTblEntry **top_rte, int *top_rti,
+                       RangeTblEntry **right_rte, int *right_rti,
+                       List **namespace);
 extern Node *transformWhereClause(ParseState *pstate, Node *clause,
                     ParseExprKind exprKind, const char *constructName);
 extern Node *transformLimitClause(ParseState *pstate, Node *clause,
 
    EXPR_KIND_INSERT_TARGET,    /* INSERT target list item */
    EXPR_KIND_UPDATE_SOURCE,    /* UPDATE assignment source item */
    EXPR_KIND_UPDATE_TARGET,    /* UPDATE assignment target item */
+   EXPR_KIND_MERGE_WHEN_AND,   /* MERGE WHEN ... AND condition */
    EXPR_KIND_GROUP_BY,         /* GROUP BY */
    EXPR_KIND_ORDER_BY,         /* ORDER BY */
    EXPR_KIND_DISTINCT_ON,      /* DISTINCT ON */
  * p_parent_cte: CommonTableExpr that immediately contains the current query,
  * if any.
  *
- * p_target_relation: target relation, if query is INSERT, UPDATE, or DELETE.
+ * p_target_relation: target relation, if query is INSERT/UPDATE/DELETE/MERGE
  *
  * p_target_rangetblentry: target relation's entry in the rtable list.
  *
    List       *p_ctenamespace; /* current namespace for common table exprs */
    List       *p_future_ctes;  /* common table exprs not yet in namespace */
    CommonTableExpr *p_parent_cte;  /* this query's containing CTE */
-   Relation    p_target_relation;  /* INSERT/UPDATE/DELETE target rel */
+   Relation    p_target_relation;  /* INSERT/UPDATE/DELETE/MERGE target rel */
    RangeTblEntry *p_target_rangetblentry;  /* target rel's RTE */
    bool        p_is_insert;    /* process assignment like INSERT not UPDATE */
    List       *p_windowdefs;   /* raw representations of window clauses */
 
 extern Node *build_column_default(Relation rel, int attrno);
 extern void rewriteTargetListUD(Query *parsetree, RangeTblEntry *target_rte,
                    Relation target_relation);
+extern void rewriteTargetListMerge(Query *parsetree, Relation target_relation);
 
 extern Query *get_view_query(Relation view);
 extern const char *view_query_is_auto_updatable(Query *viewquery,
 
 
 /*
  * PQcmdTuples -
- * If the last command was INSERT/UPDATE/DELETE/MOVE/FETCH/COPY, return
- * a string containing the number of inserted/affected tuples. If not,
- * return "".
+ * If the last command was INSERT/UPDATE/DELETE/MERGE/MOVE/FETCH/COPY,
+ * return a string containing the number of inserted/affected tuples.
+ * If not, return "".
  *
  * XXX: this should probably return an int
  */
             strncmp(res->cmdStatus, "DELETE ", 7) == 0 ||
             strncmp(res->cmdStatus, "UPDATE ", 7) == 0)
        p = res->cmdStatus + 7;
-   else if (strncmp(res->cmdStatus, "FETCH ", 6) == 0)
+   else if (strncmp(res->cmdStatus, "FETCH ", 6) == 0 ||
+            strncmp(res->cmdStatus, "MERGE ", 6) == 0)
        p = res->cmdStatus + 6;
    else if (strncmp(res->cmdStatus, "MOVE ", 5) == 0 ||
             strncmp(res->cmdStatus, "COPY ", 5) == 0)
 
 
    /*
     * On the first call for this statement generate the plan, and detect
-    * whether the statement is INSERT/UPDATE/DELETE
+    * whether the statement is INSERT/UPDATE/DELETE/MERGE
     */
    if (expr->plan == NULL)
    {
                {
                    if (q->commandType == CMD_INSERT ||
                        q->commandType == CMD_UPDATE ||
+                       q->commandType == CMD_MERGE ||
                        q->commandType == CMD_DELETE)
                        stmt->mod_stmt = true;
                }
        case SPI_OK_INSERT_RETURNING:
        case SPI_OK_UPDATE_RETURNING:
        case SPI_OK_DELETE_RETURNING:
+       case SPI_OK_MERGE:
            Assert(stmt->mod_stmt);
            exec_set_found(estate, (SPI_processed != 0));
            break;
        case SPI_OK_INSERT_RETURNING:
        case SPI_OK_UPDATE_RETURNING:
        case SPI_OK_DELETE_RETURNING:
+       case SPI_OK_MERGE:
        case SPI_OK_UTILITY:
        case SPI_OK_REWRITTEN:
            break;
 
 %token <keyword>   K_LAST
 %token <keyword>   K_LOG
 %token <keyword>   K_LOOP
+%token <keyword>   K_MERGE
 %token <keyword>   K_MESSAGE
 %token <keyword>   K_MESSAGE_TEXT
 %token <keyword>   K_MOVE
                    {
                        $$ = make_execsql_stmt(K_INSERT, @1);
                    }
+               | K_MERGE
+                   {
+                       $$ = make_execsql_stmt(K_MERGE, @1);
+                   }
                | T_WORD
                    {
                        int         tok;
                | K_IS
                | K_LAST
                | K_LOG
+               | K_MERGE
                | K_MESSAGE
                | K_MESSAGE_TEXT
                | K_MOVE
        {
            if (prev_tok == K_INSERT)
                continue;       /* INSERT INTO is not an INTO-target */
+           if (prev_tok == K_MERGE)
+               continue;       /* MERGE INTO is not an INTO-target */
            if (firsttoken == K_IMPORT)
                continue;       /* IMPORT ... INTO is not an INTO-target */
            if (have_into)
 
    PG_KEYWORD("is", K_IS, UNRESERVED_KEYWORD)
    PG_KEYWORD("last", K_LAST, UNRESERVED_KEYWORD)
    PG_KEYWORD("log", K_LOG, UNRESERVED_KEYWORD)
+   PG_KEYWORD("merge", K_MERGE, UNRESERVED_KEYWORD)
    PG_KEYWORD("message", K_MESSAGE, UNRESERVED_KEYWORD)
    PG_KEYWORD("message_text", K_MESSAGE_TEXT, UNRESERVED_KEYWORD)
    PG_KEYWORD("move", K_MOVE, UNRESERVED_KEYWORD)
 
    PLpgSQL_stmt_type cmd_type;
    int         lineno;
    PLpgSQL_expr *sqlstmt;
-   bool        mod_stmt;       /* is the stmt INSERT/UPDATE/DELETE?  Note:
-                                * mod_stmt is set when we plan the query */
+   bool        mod_stmt;       /* is the stmt INSERT/UPDATE/DELETE/MERGE?
+                                * Note mod_stmt is set when we plan the query */
    bool        into;           /* INTO supplied? */
    bool        strict;         /* INTO STRICT flag */
    PLpgSQL_variable *target;   /* INTO target (record or row) */
 
 test: insert-conflict-do-update-2
 test: insert-conflict-do-update-3
 test: insert-conflict-toast
+test: merge-insert-update
+test: merge-delete
+test: merge-update
+test: merge-match-recheck
 test: delete-abort-savept
 test: delete-abort-savept-2
 test: aborted-keyrevoke
 
 ) FOR VALUES FROM ('2016-07-01') TO ('2016-08-01'); -- error
 ERROR:  identity columns are not supported on partitions
 DROP TABLE itest_parent;
+-- MERGE tests
+CREATE TABLE itest14 (a int GENERATED ALWAYS AS IDENTITY, b text);
+CREATE TABLE itest15 (a int GENERATED BY DEFAULT AS IDENTITY, b text);
+MERGE INTO itest14 t
+USING (SELECT 10 AS s_a, 'inserted by merge' AS s_b) s
+ON t.a = s.s_a
+WHEN NOT MATCHED THEN
+   INSERT (a, b) VALUES (s.s_a, s.s_b);
+ERROR:  cannot insert into column "a"
+DETAIL:  Column "a" is an identity column defined as GENERATED ALWAYS.
+HINT:  Use OVERRIDING SYSTEM VALUE to override.
+MERGE INTO itest14 t
+USING (SELECT 20 AS s_a, 'inserted by merge' AS s_b) s
+ON t.a = s.s_a
+WHEN NOT MATCHED THEN
+   INSERT (a, b) OVERRIDING USER VALUE VALUES (s.s_a, s.s_b);
+ERROR:  cannot insert into column "a"
+DETAIL:  Column "a" is an identity column defined as GENERATED ALWAYS.
+HINT:  Use OVERRIDING SYSTEM VALUE to override.
+MERGE INTO itest14 t
+USING (SELECT 30 AS s_a, 'inserted by merge' AS s_b) s
+ON t.a = s.s_a
+WHEN NOT MATCHED THEN
+   INSERT (a, b) OVERRIDING SYSTEM VALUE VALUES (s.s_a, s.s_b);
+MERGE INTO itest15 t
+USING (SELECT 10 AS s_a, 'inserted by merge' AS s_b) s
+ON t.a = s.s_a
+WHEN NOT MATCHED THEN
+   INSERT (a, b) VALUES (s.s_a, s.s_b);
+MERGE INTO itest15 t
+USING (SELECT 20 AS s_a, 'inserted by merge' AS s_b) s
+ON t.a = s.s_a
+WHEN NOT MATCHED THEN
+   INSERT (a, b) OVERRIDING USER VALUE VALUES (s.s_a, s.s_b);
+MERGE INTO itest15 t
+USING (SELECT 30 AS s_a, 'inserted by merge' AS s_b) s
+ON t.a = s.s_a
+WHEN NOT MATCHED THEN
+   INSERT (a, b) OVERRIDING SYSTEM VALUE VALUES (s.s_a, s.s_b);
+SELECT * FROM itest14;
+ a  |         b         
+----+-------------------
+ 30 | inserted by merge
+(1 row)
+
+SELECT * FROM itest15;
+ a  |         b         
+----+-------------------
+ 10 | inserted by merge
+  1 | inserted by merge
+ 30 | inserted by merge
+(3 rows)
+
+DROP TABLE itest14;
+DROP TABLE itest15;
 
 (0 rows)
 
 COPY atest6 TO stdout; -- ok
+-- test column privileges with MERGE
+SET SESSION AUTHORIZATION regress_priv_user1;
+CREATE TABLE mtarget (a int, b text);
+CREATE TABLE msource (a int, b text);
+INSERT INTO mtarget VALUES (1, 'init1'), (2, 'init2');
+INSERT INTO msource VALUES (1, 'source1'), (2, 'source2'), (3, 'source3');
+GRANT SELECT (a) ON msource TO regress_priv_user4;
+GRANT SELECT (a) ON mtarget TO regress_priv_user4;
+GRANT INSERT (a,b) ON mtarget TO regress_priv_user4;
+GRANT UPDATE (b) ON mtarget TO regress_priv_user4;
+SET SESSION AUTHORIZATION regress_priv_user4;
+--
+-- test source privileges
+--
+-- fail (no SELECT priv on s.b)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+   UPDATE SET b = s.b
+WHEN NOT MATCHED THEN
+   INSERT VALUES (a, NULL);
+ERROR:  permission denied for table msource
+-- fail (s.b used in the INSERTed values)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+   UPDATE SET b = 'x'
+WHEN NOT MATCHED THEN
+   INSERT VALUES (a, b);
+ERROR:  permission denied for table msource
+-- fail (s.b used in the WHEN quals)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED AND s.b = 'x' THEN
+   UPDATE SET b = 'x'
+WHEN NOT MATCHED THEN
+   INSERT VALUES (a, NULL);
+ERROR:  permission denied for table msource
+-- this should be ok since only s.a is accessed
+BEGIN;
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+   UPDATE SET b = 'ok'
+WHEN NOT MATCHED THEN
+   INSERT VALUES (a, NULL);
+ROLLBACK;
+SET SESSION AUTHORIZATION regress_priv_user1;
+GRANT SELECT (b) ON msource TO regress_priv_user4;
+SET SESSION AUTHORIZATION regress_priv_user4;
+-- should now be ok
+BEGIN;
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+   UPDATE SET b = s.b
+WHEN NOT MATCHED THEN
+   INSERT VALUES (a, b);
+ROLLBACK;
+--
+-- test target privileges
+--
+-- fail (no SELECT priv on t.b)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+   UPDATE SET b = t.b
+WHEN NOT MATCHED THEN
+   INSERT VALUES (a, NULL);
+ERROR:  permission denied for table mtarget
+-- fail (no UPDATE on t.a)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+   UPDATE SET b = s.b, a = t.a + 1
+WHEN NOT MATCHED THEN
+   INSERT VALUES (a, b);
+ERROR:  permission denied for table mtarget
+-- fail (no SELECT on t.b)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED AND t.b IS NOT NULL THEN
+   UPDATE SET b = s.b
+WHEN NOT MATCHED THEN
+   INSERT VALUES (a, b);
+ERROR:  permission denied for table mtarget
+-- ok
+BEGIN;
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+   UPDATE SET b = s.b;
+ROLLBACK;
+-- fail (no DELETE)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED AND t.b IS NOT NULL THEN
+   DELETE;
+ERROR:  permission denied for table mtarget
+-- grant delete privileges
+SET SESSION AUTHORIZATION regress_priv_user1;
+GRANT DELETE ON mtarget TO regress_priv_user4;
+-- should be ok now
+BEGIN;
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED AND t.b IS NOT NULL THEN
+   DELETE;
+ROLLBACK;
 -- check error reporting with column privs
 SET SESSION AUTHORIZATION regress_priv_user1;
 CREATE TABLE t1 (c1 int, c2 int, c3 int check (c3 < 5), primary key (c1, c2));
 
 INSERT INTO document VALUES (1, (SELECT cid from category WHERE cname = 'novel'), 1, 'regress_rls_bob', 'my first novel')
     ON CONFLICT (did) DO UPDATE SET dauthor = 'regress_rls_carol';
 ERROR:  new row violates row-level security policy for table "document"
+--
+-- MERGE
+--
+RESET SESSION AUTHORIZATION;
+DROP POLICY p3_with_all ON document;
+ALTER TABLE document ADD COLUMN dnotes text DEFAULT '';
+-- all documents are readable
+CREATE POLICY p1 ON document FOR SELECT USING (true);
+-- one may insert documents only authored by them
+CREATE POLICY p2 ON document FOR INSERT WITH CHECK (dauthor = current_user);
+-- one may only update documents in 'novel' category
+CREATE POLICY p3 ON document FOR UPDATE
+  USING (cid = (SELECT cid from category WHERE cname = 'novel'))
+  WITH CHECK (dauthor = current_user);
+-- one may only delete documents in 'manga' category
+CREATE POLICY p4 ON document FOR DELETE
+  USING (cid = (SELECT cid from category WHERE cname = 'manga'));
+SELECT * FROM document;
+ did | cid | dlevel |      dauthor      |              dtitle              | dnotes 
+-----+-----+--------+-------------------+----------------------------------+--------
+   1 |  11 |      1 | regress_rls_bob   | my first novel                   | 
+   3 |  22 |      2 | regress_rls_bob   | my science fiction               | 
+   4 |  44 |      1 | regress_rls_bob   | my first manga                   | 
+   5 |  44 |      2 | regress_rls_bob   | my second manga                  | 
+   6 |  22 |      1 | regress_rls_carol | great science fiction            | 
+   7 |  33 |      2 | regress_rls_carol | great technology book            | 
+   8 |  44 |      1 | regress_rls_carol | great manga                      | 
+   9 |  22 |      1 | regress_rls_dave  | awesome science fiction          | 
+  10 |  33 |      2 | regress_rls_dave  | awesome technology book          | 
+  11 |  33 |      1 | regress_rls_carol | hoge                             | 
+  33 |  22 |      1 | regress_rls_bob   | okay science fiction             | 
+   2 |  11 |      2 | regress_rls_bob   | my first novel                   | 
+  78 |  33 |      1 | regress_rls_bob   | some technology novel            | 
+  79 |  33 |      1 | regress_rls_bob   | technology book, can only insert | 
+(14 rows)
+
+SET SESSION AUTHORIZATION regress_rls_bob;
+-- Fails, since update violates WITH CHECK qual on dauthor
+MERGE INTO document d
+USING (SELECT 1 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+   UPDATE SET dnotes = dnotes || ' notes added by merge1 ', dauthor = 'regress_rls_alice';
+ERROR:  new row violates row-level security policy for table "document"
+-- Should be OK since USING and WITH CHECK quals pass
+MERGE INTO document d
+USING (SELECT 1 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+   UPDATE SET dnotes = dnotes || ' notes added by merge2 ';
+-- Even when dauthor is updated explicitly, but to the existing value
+MERGE INTO document d
+USING (SELECT 1 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+   UPDATE SET dnotes = dnotes || ' notes added by merge3 ', dauthor = 'regress_rls_bob';
+-- There is a MATCH for did = 3, but UPDATE's USING qual does not allow
+-- updating an item in category 'science fiction'
+MERGE INTO document d
+USING (SELECT 3 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+   UPDATE SET dnotes = dnotes || ' notes added by merge ';
+ERROR:  target row violates row-level security policy (USING expression) for table "document"
+-- The same thing with DELETE action, but fails again because no permissions
+-- to delete items in 'science fiction' category that did 3 belongs to.
+MERGE INTO document d
+USING (SELECT 3 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+   DELETE;
+ERROR:  target row violates row-level security policy (USING expression) for table "document"
+-- Document with did 4 belongs to 'manga' category which is allowed for
+-- deletion. But this fails because the UPDATE action is matched first and
+-- UPDATE policy does not allow updation in the category.
+MERGE INTO document d
+USING (SELECT 4 as sdid) s
+ON did = s.sdid
+WHEN MATCHED AND dnotes = '' THEN
+   UPDATE SET dnotes = dnotes || ' notes added by merge '
+WHEN MATCHED THEN
+   DELETE;
+ERROR:  target row violates row-level security policy (USING expression) for table "document"
+-- UPDATE action is not matched this time because of the WHEN AND qual.
+-- DELETE still fails because role regress_rls_bob does not have SELECT
+-- privileges on 'manga' category row in the category table.
+MERGE INTO document d
+USING (SELECT 4 as sdid) s
+ON did = s.sdid
+WHEN MATCHED AND dnotes <> '' THEN
+   UPDATE SET dnotes = dnotes || ' notes added by merge '
+WHEN MATCHED THEN
+   DELETE;
+ERROR:  target row violates row-level security policy (USING expression) for table "document"
+SELECT * FROM document WHERE did = 4;
+ did | cid | dlevel |     dauthor     |     dtitle     | dnotes 
+-----+-----+--------+-----------------+----------------+--------
+   4 |  44 |      1 | regress_rls_bob | my first manga | 
+(1 row)
+
+-- Switch to regress_rls_carol role and try the DELETE again. It should succeed
+-- this time
+RESET SESSION AUTHORIZATION;
+SET SESSION AUTHORIZATION regress_rls_carol;
+MERGE INTO document d
+USING (SELECT 4 as sdid) s
+ON did = s.sdid
+WHEN MATCHED AND dnotes <> '' THEN
+   UPDATE SET dnotes = dnotes || ' notes added by merge '
+WHEN MATCHED THEN
+   DELETE;
+-- Switch back to regress_rls_bob role
+RESET SESSION AUTHORIZATION;
+SET SESSION AUTHORIZATION regress_rls_bob;
+-- Try INSERT action. This fails because we are trying to insert
+-- dauthor = regress_rls_dave and INSERT's WITH CHECK does not allow
+-- that
+MERGE INTO document d
+USING (SELECT 12 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+   DELETE
+WHEN NOT MATCHED THEN
+   INSERT VALUES (12, 11, 1, 'regress_rls_dave', 'another novel');
+ERROR:  new row violates row-level security policy for table "document"
+-- This should be fine
+MERGE INTO document d
+USING (SELECT 12 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+   DELETE
+WHEN NOT MATCHED THEN
+   INSERT VALUES (12, 11, 1, 'regress_rls_bob', 'another novel');
+-- ok
+MERGE INTO document d
+USING (SELECT 1 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+   UPDATE SET dnotes = dnotes || ' notes added by merge4 '
+WHEN NOT MATCHED THEN
+   INSERT VALUES (12, 11, 1, 'regress_rls_bob', 'another novel');
+-- drop and create a new SELECT policy which prevents us from reading
+-- any document except with category 'magna'
+RESET SESSION AUTHORIZATION;
+DROP POLICY p1 ON document;
+CREATE POLICY p1 ON document FOR SELECT
+  USING (cid = (SELECT cid from category WHERE cname = 'manga'));
+SET SESSION AUTHORIZATION regress_rls_bob;
+-- MERGE can no longer see the matching row and hence attempts the
+-- NOT MATCHED action, which results in unique key violation
+MERGE INTO document d
+USING (SELECT 1 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+   UPDATE SET dnotes = dnotes || ' notes added by merge5 '
+WHEN NOT MATCHED THEN
+   INSERT VALUES (12, 11, 1, 'regress_rls_bob', 'another novel');
+ERROR:  duplicate key value violates unique constraint "document_pkey"
+RESET SESSION AUTHORIZATION;
+-- drop the restrictive SELECT policy so that we can look at the
+-- final state of the table
+DROP POLICY p1 ON document;
+-- Just check everything went per plan
+SELECT * FROM document;
+ did | cid | dlevel |      dauthor      |              dtitle              |                                dnotes                                 
+-----+-----+--------+-------------------+----------------------------------+-----------------------------------------------------------------------
+   3 |  22 |      2 | regress_rls_bob   | my science fiction               | 
+   5 |  44 |      2 | regress_rls_bob   | my second manga                  | 
+   6 |  22 |      1 | regress_rls_carol | great science fiction            | 
+   7 |  33 |      2 | regress_rls_carol | great technology book            | 
+   8 |  44 |      1 | regress_rls_carol | great manga                      | 
+   9 |  22 |      1 | regress_rls_dave  | awesome science fiction          | 
+  10 |  33 |      2 | regress_rls_dave  | awesome technology book          | 
+  11 |  33 |      1 | regress_rls_carol | hoge                             | 
+  33 |  22 |      1 | regress_rls_bob   | okay science fiction             | 
+   2 |  11 |      2 | regress_rls_bob   | my first novel                   | 
+  78 |  33 |      1 | regress_rls_bob   | some technology novel            | 
+  79 |  33 |      1 | regress_rls_bob   | technology book, can only insert | 
+  12 |  11 |      1 | regress_rls_bob   | another novel                    | 
+   1 |  11 |      1 | regress_rls_bob   | my first novel                   |  notes added by merge2  notes added by merge3  notes added by merge4 
+(14 rows)
+
 --
 -- ROLE/GROUP
 --
 
 ALTER RULE rules_parted_table_insert ON rules_parted_table RENAME TO rules_parted_table_insert_redirect;
 DROP TABLE rules_parted_table;
 --
+-- test MERGE
+--
+CREATE TABLE rule_merge1 (a int, b text);
+CREATE TABLE rule_merge2 (a int, b text);
+CREATE RULE rule1 AS ON INSERT TO rule_merge1
+   DO INSTEAD INSERT INTO rule_merge2 VALUES (NEW.*);
+CREATE RULE rule2 AS ON UPDATE TO rule_merge1
+   DO INSTEAD UPDATE rule_merge2 SET a = NEW.a, b = NEW.b
+   WHERE a = OLD.a;
+CREATE RULE rule3 AS ON DELETE TO rule_merge1
+   DO INSTEAD DELETE FROM rule_merge2 WHERE a = OLD.a;
+-- MERGE not supported for table with rules
+MERGE INTO rule_merge1 t USING (SELECT 1 AS a) s
+   ON t.a = s.a
+   WHEN MATCHED AND t.a < 2 THEN
+       UPDATE SET b = b || ' updated by merge'
+   WHEN MATCHED AND t.a > 2 THEN
+       DELETE
+   WHEN NOT MATCHED THEN
+       INSERT VALUES (s.a, '');
+ERROR:  MERGE is not supported for relations with rules
+-- should be ok with the other table though
+MERGE INTO rule_merge2 t USING (SELECT 1 AS a) s
+   ON t.a = s.a
+   WHEN MATCHED AND t.a < 2 THEN
+       UPDATE SET b = b || ' updated by merge'
+   WHEN MATCHED AND t.a > 2 THEN
+       DELETE
+   WHEN NOT MATCHED THEN
+       INSERT VALUES (s.a, '');
+--
 -- Test enabling/disabling
 --
 CREATE TABLE ruletest1 (a int);
 
 NOTICE:  trigger_func(self_ref) called: action = DELETE, when = BEFORE, level = STATEMENT
 NOTICE:  trigger = self_ref_s_trig, old table = (1,), (2,1), (3,2), (4,3)
 drop table self_ref;
+--
+-- test transition tables with MERGE
+--
+create table merge_target_table (a int primary key, b text);
+create trigger merge_target_table_insert_trig
+  after insert on merge_target_table referencing new table as new_table
+  for each statement execute procedure dump_insert();
+create trigger merge_target_table_update_trig
+  after update on merge_target_table referencing old table as old_table new table as new_table
+  for each statement execute procedure dump_update();
+create trigger merge_target_table_delete_trig
+  after delete on merge_target_table referencing old table as old_table
+  for each statement execute procedure dump_delete();
+create table merge_source_table (a int, b text);
+insert into merge_source_table
+  values (1, 'initial1'), (2, 'initial2'),
+        (3, 'initial3'), (4, 'initial4');
+merge into merge_target_table t
+using merge_source_table s
+on t.a = s.a
+when not matched then
+  insert values (a, b);
+NOTICE:  trigger = merge_target_table_insert_trig, new table = (1,initial1), (2,initial2), (3,initial3), (4,initial4)
+merge into merge_target_table t
+using merge_source_table s
+on t.a = s.a
+when matched and s.a <= 2 then
+   update set b = t.b || ' updated by merge'
+when matched and s.a > 2 then
+   delete
+when not matched then
+  insert values (a, b);
+NOTICE:  trigger = merge_target_table_delete_trig, old table = (3,initial3), (4,initial4)
+NOTICE:  trigger = merge_target_table_update_trig, old table = (1,initial1), (2,initial2), new table = (1,"initial1 updated by merge"), (2,"initial2 updated by merge")
+NOTICE:  trigger = merge_target_table_insert_trig, new table = <NULL>
+merge into merge_target_table t
+using merge_source_table s
+on t.a = s.a
+when matched and s.a <= 2 then
+   update set b = t.b || ' updated again by merge'
+when matched and s.a > 2 then
+   delete
+when not matched then
+  insert values (a, b);
+NOTICE:  trigger = merge_target_table_delete_trig, old table = <NULL>
+NOTICE:  trigger = merge_target_table_update_trig, old table = (1,"initial1 updated by merge"), (2,"initial2 updated by merge"), new table = (1,"initial1 updated by merge updated again by merge"), (2,"initial2 updated by merge updated again by merge")
+NOTICE:  trigger = merge_target_table_insert_trig, new table = (3,initial3), (4,initial4)
+drop table merge_source_table, merge_target_table;
 -- cleanup
 drop function dump_insert();
 drop function dump_update();
 
 # ----------
 # Another group of parallel tests
 # ----------
-test: brin gin gist spgist privileges init_privs security_label collate matview lock replica_identity rowsecurity object_address tablesample groupingsets drop_operator password func_index
+test: brin gin gist spgist privileges init_privs security_label collate matview lock replica_identity rowsecurity object_address tablesample groupingsets drop_operator password func_index merge
 
 # ----------
 # Another group of parallel tests
 
 test: groupingsets
 test: drop_operator
 test: password
+test: merge
 test: alter_generic
 test: alter_operator
 test: misc
 
     f3 WITH OPTIONS GENERATED ALWAYS AS IDENTITY
 ) FOR VALUES FROM ('2016-07-01') TO ('2016-08-01'); -- error
 DROP TABLE itest_parent;
+
+-- MERGE tests
+CREATE TABLE itest14 (a int GENERATED ALWAYS AS IDENTITY, b text);
+CREATE TABLE itest15 (a int GENERATED BY DEFAULT AS IDENTITY, b text);
+
+MERGE INTO itest14 t
+USING (SELECT 10 AS s_a, 'inserted by merge' AS s_b) s
+ON t.a = s.s_a
+WHEN NOT MATCHED THEN
+   INSERT (a, b) VALUES (s.s_a, s.s_b);
+
+MERGE INTO itest14 t
+USING (SELECT 20 AS s_a, 'inserted by merge' AS s_b) s
+ON t.a = s.s_a
+WHEN NOT MATCHED THEN
+   INSERT (a, b) OVERRIDING USER VALUE VALUES (s.s_a, s.s_b);
+
+MERGE INTO itest14 t
+USING (SELECT 30 AS s_a, 'inserted by merge' AS s_b) s
+ON t.a = s.s_a
+WHEN NOT MATCHED THEN
+   INSERT (a, b) OVERRIDING SYSTEM VALUE VALUES (s.s_a, s.s_b);
+
+MERGE INTO itest15 t
+USING (SELECT 10 AS s_a, 'inserted by merge' AS s_b) s
+ON t.a = s.s_a
+WHEN NOT MATCHED THEN
+   INSERT (a, b) VALUES (s.s_a, s.s_b);
+
+MERGE INTO itest15 t
+USING (SELECT 20 AS s_a, 'inserted by merge' AS s_b) s
+ON t.a = s.s_a
+WHEN NOT MATCHED THEN
+   INSERT (a, b) OVERRIDING USER VALUE VALUES (s.s_a, s.s_b);
+
+MERGE INTO itest15 t
+USING (SELECT 30 AS s_a, 'inserted by merge' AS s_b) s
+ON t.a = s.s_a
+WHEN NOT MATCHED THEN
+   INSERT (a, b) OVERRIDING SYSTEM VALUE VALUES (s.s_a, s.s_b);
+
+SELECT * FROM itest14;
+SELECT * FROM itest15;
+DROP TABLE itest14;
+DROP TABLE itest15;
 
 SELECT atest6 FROM atest6; -- ok
 COPY atest6 TO stdout; -- ok
 
+-- test column privileges with MERGE
+SET SESSION AUTHORIZATION regress_priv_user1;
+CREATE TABLE mtarget (a int, b text);
+CREATE TABLE msource (a int, b text);
+INSERT INTO mtarget VALUES (1, 'init1'), (2, 'init2');
+INSERT INTO msource VALUES (1, 'source1'), (2, 'source2'), (3, 'source3');
+
+GRANT SELECT (a) ON msource TO regress_priv_user4;
+GRANT SELECT (a) ON mtarget TO regress_priv_user4;
+GRANT INSERT (a,b) ON mtarget TO regress_priv_user4;
+GRANT UPDATE (b) ON mtarget TO regress_priv_user4;
+
+SET SESSION AUTHORIZATION regress_priv_user4;
+
+--
+-- test source privileges
+--
+
+-- fail (no SELECT priv on s.b)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+   UPDATE SET b = s.b
+WHEN NOT MATCHED THEN
+   INSERT VALUES (a, NULL);
+
+-- fail (s.b used in the INSERTed values)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+   UPDATE SET b = 'x'
+WHEN NOT MATCHED THEN
+   INSERT VALUES (a, b);
+
+-- fail (s.b used in the WHEN quals)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED AND s.b = 'x' THEN
+   UPDATE SET b = 'x'
+WHEN NOT MATCHED THEN
+   INSERT VALUES (a, NULL);
+
+-- this should be ok since only s.a is accessed
+BEGIN;
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+   UPDATE SET b = 'ok'
+WHEN NOT MATCHED THEN
+   INSERT VALUES (a, NULL);
+ROLLBACK;
+
+SET SESSION AUTHORIZATION regress_priv_user1;
+GRANT SELECT (b) ON msource TO regress_priv_user4;
+SET SESSION AUTHORIZATION regress_priv_user4;
+
+-- should now be ok
+BEGIN;
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+   UPDATE SET b = s.b
+WHEN NOT MATCHED THEN
+   INSERT VALUES (a, b);
+ROLLBACK;
+
+--
+-- test target privileges
+--
+
+-- fail (no SELECT priv on t.b)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+   UPDATE SET b = t.b
+WHEN NOT MATCHED THEN
+   INSERT VALUES (a, NULL);
+
+-- fail (no UPDATE on t.a)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+   UPDATE SET b = s.b, a = t.a + 1
+WHEN NOT MATCHED THEN
+   INSERT VALUES (a, b);
+
+-- fail (no SELECT on t.b)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED AND t.b IS NOT NULL THEN
+   UPDATE SET b = s.b
+WHEN NOT MATCHED THEN
+   INSERT VALUES (a, b);
+
+-- ok
+BEGIN;
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED THEN
+   UPDATE SET b = s.b;
+ROLLBACK;
+
+-- fail (no DELETE)
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED AND t.b IS NOT NULL THEN
+   DELETE;
+
+-- grant delete privileges
+SET SESSION AUTHORIZATION regress_priv_user1;
+GRANT DELETE ON mtarget TO regress_priv_user4;
+-- should be ok now
+BEGIN;
+MERGE INTO mtarget t USING msource s ON t.a = s.a
+WHEN MATCHED AND t.b IS NOT NULL THEN
+   DELETE;
+ROLLBACK;
+
 -- check error reporting with column privs
 SET SESSION AUTHORIZATION regress_priv_user1;
 CREATE TABLE t1 (c1 int, c2 int, c3 int check (c3 < 5), primary key (c1, c2));
 
 INSERT INTO document VALUES (1, (SELECT cid from category WHERE cname = 'novel'), 1, 'regress_rls_bob', 'my first novel')
     ON CONFLICT (did) DO UPDATE SET dauthor = 'regress_rls_carol';
 
+--
+-- MERGE
+--
+RESET SESSION AUTHORIZATION;
+DROP POLICY p3_with_all ON document;
+
+ALTER TABLE document ADD COLUMN dnotes text DEFAULT '';
+-- all documents are readable
+CREATE POLICY p1 ON document FOR SELECT USING (true);
+-- one may insert documents only authored by them
+CREATE POLICY p2 ON document FOR INSERT WITH CHECK (dauthor = current_user);
+-- one may only update documents in 'novel' category
+CREATE POLICY p3 ON document FOR UPDATE
+  USING (cid = (SELECT cid from category WHERE cname = 'novel'))
+  WITH CHECK (dauthor = current_user);
+-- one may only delete documents in 'manga' category
+CREATE POLICY p4 ON document FOR DELETE
+  USING (cid = (SELECT cid from category WHERE cname = 'manga'));
+
+SELECT * FROM document;
+
+SET SESSION AUTHORIZATION regress_rls_bob;
+
+-- Fails, since update violates WITH CHECK qual on dauthor
+MERGE INTO document d
+USING (SELECT 1 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+   UPDATE SET dnotes = dnotes || ' notes added by merge1 ', dauthor = 'regress_rls_alice';
+
+-- Should be OK since USING and WITH CHECK quals pass
+MERGE INTO document d
+USING (SELECT 1 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+   UPDATE SET dnotes = dnotes || ' notes added by merge2 ';
+
+-- Even when dauthor is updated explicitly, but to the existing value
+MERGE INTO document d
+USING (SELECT 1 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+   UPDATE SET dnotes = dnotes || ' notes added by merge3 ', dauthor = 'regress_rls_bob';
+
+-- There is a MATCH for did = 3, but UPDATE's USING qual does not allow
+-- updating an item in category 'science fiction'
+MERGE INTO document d
+USING (SELECT 3 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+   UPDATE SET dnotes = dnotes || ' notes added by merge ';
+
+-- The same thing with DELETE action, but fails again because no permissions
+-- to delete items in 'science fiction' category that did 3 belongs to.
+MERGE INTO document d
+USING (SELECT 3 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+   DELETE;
+
+-- Document with did 4 belongs to 'manga' category which is allowed for
+-- deletion. But this fails because the UPDATE action is matched first and
+-- UPDATE policy does not allow updation in the category.
+MERGE INTO document d
+USING (SELECT 4 as sdid) s
+ON did = s.sdid
+WHEN MATCHED AND dnotes = '' THEN
+   UPDATE SET dnotes = dnotes || ' notes added by merge '
+WHEN MATCHED THEN
+   DELETE;
+
+-- UPDATE action is not matched this time because of the WHEN AND qual.
+-- DELETE still fails because role regress_rls_bob does not have SELECT
+-- privileges on 'manga' category row in the category table.
+MERGE INTO document d
+USING (SELECT 4 as sdid) s
+ON did = s.sdid
+WHEN MATCHED AND dnotes <> '' THEN
+   UPDATE SET dnotes = dnotes || ' notes added by merge '
+WHEN MATCHED THEN
+   DELETE;
+
+SELECT * FROM document WHERE did = 4;
+
+-- Switch to regress_rls_carol role and try the DELETE again. It should succeed
+-- this time
+RESET SESSION AUTHORIZATION;
+SET SESSION AUTHORIZATION regress_rls_carol;
+
+MERGE INTO document d
+USING (SELECT 4 as sdid) s
+ON did = s.sdid
+WHEN MATCHED AND dnotes <> '' THEN
+   UPDATE SET dnotes = dnotes || ' notes added by merge '
+WHEN MATCHED THEN
+   DELETE;
+
+-- Switch back to regress_rls_bob role
+RESET SESSION AUTHORIZATION;
+SET SESSION AUTHORIZATION regress_rls_bob;
+
+-- Try INSERT action. This fails because we are trying to insert
+-- dauthor = regress_rls_dave and INSERT's WITH CHECK does not allow
+-- that
+MERGE INTO document d
+USING (SELECT 12 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+   DELETE
+WHEN NOT MATCHED THEN
+   INSERT VALUES (12, 11, 1, 'regress_rls_dave', 'another novel');
+
+-- This should be fine
+MERGE INTO document d
+USING (SELECT 12 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+   DELETE
+WHEN NOT MATCHED THEN
+   INSERT VALUES (12, 11, 1, 'regress_rls_bob', 'another novel');
+
+-- ok
+MERGE INTO document d
+USING (SELECT 1 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+   UPDATE SET dnotes = dnotes || ' notes added by merge4 '
+WHEN NOT MATCHED THEN
+   INSERT VALUES (12, 11, 1, 'regress_rls_bob', 'another novel');
+
+-- drop and create a new SELECT policy which prevents us from reading
+-- any document except with category 'magna'
+RESET SESSION AUTHORIZATION;
+DROP POLICY p1 ON document;
+CREATE POLICY p1 ON document FOR SELECT
+  USING (cid = (SELECT cid from category WHERE cname = 'manga'));
+
+SET SESSION AUTHORIZATION regress_rls_bob;
+
+-- MERGE can no longer see the matching row and hence attempts the
+-- NOT MATCHED action, which results in unique key violation
+MERGE INTO document d
+USING (SELECT 1 as sdid) s
+ON did = s.sdid
+WHEN MATCHED THEN
+   UPDATE SET dnotes = dnotes || ' notes added by merge5 '
+WHEN NOT MATCHED THEN
+   INSERT VALUES (12, 11, 1, 'regress_rls_bob', 'another novel');
+
+RESET SESSION AUTHORIZATION;
+-- drop the restrictive SELECT policy so that we can look at the
+-- final state of the table
+DROP POLICY p1 ON document;
+-- Just check everything went per plan
+SELECT * FROM document;
+
 --
 -- ROLE/GROUP
 --
 
 ALTER RULE rules_parted_table_insert ON rules_parted_table RENAME TO rules_parted_table_insert_redirect;
 DROP TABLE rules_parted_table;
 
+--
+-- test MERGE
+--
+CREATE TABLE rule_merge1 (a int, b text);
+CREATE TABLE rule_merge2 (a int, b text);
+CREATE RULE rule1 AS ON INSERT TO rule_merge1
+   DO INSTEAD INSERT INTO rule_merge2 VALUES (NEW.*);
+CREATE RULE rule2 AS ON UPDATE TO rule_merge1
+   DO INSTEAD UPDATE rule_merge2 SET a = NEW.a, b = NEW.b
+   WHERE a = OLD.a;
+CREATE RULE rule3 AS ON DELETE TO rule_merge1
+   DO INSTEAD DELETE FROM rule_merge2 WHERE a = OLD.a;
+
+-- MERGE not supported for table with rules
+MERGE INTO rule_merge1 t USING (SELECT 1 AS a) s
+   ON t.a = s.a
+   WHEN MATCHED AND t.a < 2 THEN
+       UPDATE SET b = b || ' updated by merge'
+   WHEN MATCHED AND t.a > 2 THEN
+       DELETE
+   WHEN NOT MATCHED THEN
+       INSERT VALUES (s.a, '');
+
+-- should be ok with the other table though
+MERGE INTO rule_merge2 t USING (SELECT 1 AS a) s
+   ON t.a = s.a
+   WHEN MATCHED AND t.a < 2 THEN
+       UPDATE SET b = b || ' updated by merge'
+   WHEN MATCHED AND t.a > 2 THEN
+       DELETE
+   WHEN NOT MATCHED THEN
+       INSERT VALUES (s.a, '');
+
 --
 -- Test enabling/disabling
 --
 
 
 drop table self_ref;
 
+--
+-- test transition tables with MERGE
+--
+create table merge_target_table (a int primary key, b text);
+create trigger merge_target_table_insert_trig
+  after insert on merge_target_table referencing new table as new_table
+  for each statement execute procedure dump_insert();
+create trigger merge_target_table_update_trig
+  after update on merge_target_table referencing old table as old_table new table as new_table
+  for each statement execute procedure dump_update();
+create trigger merge_target_table_delete_trig
+  after delete on merge_target_table referencing old table as old_table
+  for each statement execute procedure dump_delete();
+
+create table merge_source_table (a int, b text);
+insert into merge_source_table
+  values (1, 'initial1'), (2, 'initial2'),
+        (3, 'initial3'), (4, 'initial4');
+
+merge into merge_target_table t
+using merge_source_table s
+on t.a = s.a
+when not matched then
+  insert values (a, b);
+
+merge into merge_target_table t
+using merge_source_table s
+on t.a = s.a
+when matched and s.a <= 2 then
+   update set b = t.b || ' updated by merge'
+when matched and s.a > 2 then
+   delete
+when not matched then
+  insert values (a, b);
+
+merge into merge_target_table t
+using merge_source_table s
+on t.a = s.a
+when matched and s.a <= 2 then
+   update set b = t.b || ' updated again by merge'
+when matched and s.a > 2 then
+   delete
+when not matched then
+  insert values (a, b);
+
+drop table merge_source_table, merge_target_table;
+
 -- cleanup
 drop function dump_insert();
 drop function dump_update();
 
 MemoryContextCounters
 MemoryContextData
 MemoryContextMethods
+MergeAction
+MergeActionState
 MergeAppend
 MergeAppendPath
 MergeAppendState
 MergeJoinClause
 MergeJoinState
 MergePath
+MergeStmt
 MergeScanSelCache
 MetaCommand
 MinMaxAggInfo