Handle default tablespace in AlterTableInternal

Move handling of default tablespace for CREATE OR REPLACE MATERIALIZED
VIEW from create_ctas_internal to ATPrepSetTableSpace.  It feels cleaner
that way in my opinion by not having to resolve the tablespace name just
to pass it to AlterTableInternal.  The default table space is passed as
empty string to AlterTableInternal.

Author: ewie

src/backend/commands/createas.c

@@ -24,7 +24,6 @@
  */
 #include "postgres.h"
 
-#include "miscadmin.h"
 #include "access/heapam.h"
 #include "access/reloptions.h"
 #include "access/tableam.h"
@@ -35,7 +34,6 @@
 #include "commands/matview.h"
 #include "commands/prepare.h"
 #include "commands/tablecmds.h"
-#include "commands/tablespace.h"
 #include "commands/view.h"
 #include "executor/execdesc.h"
 #include "executor/executor.h"
@@ -160,23 +158,8 @@ create_ctas_internal(List *attrList, IntoClause *into)
 		/* tablespace */
 		atcmd = makeNode(AlterTableCmd);
 		atcmd->subtype = AT_SetTableSpace;
-		if (into->tableSpaceName != NULL)
-			atcmd->name = into->tableSpaceName;
-		else
-		{
-			Oid spcid;
-
-			/*
-			 * Resolve the name of the default or database tablespace because
-			 * we need to specify the tablespace by name.
-			 *
-			 * TODO: Move that to ATPrepSetTableSpace? Must allow AlterTableCmd.name to be NULL then.
-			 */
-			spcid = GetDefaultTablespace(RELPERSISTENCE_PERMANENT, false);
-			if (!OidIsValid(spcid))
-				spcid = MyDatabaseTableSpace;
-			atcmd->name = get_tablespace_name(spcid);
-		}
+		/* use empty string to specify default tablespace */
+		atcmd->name = into->tableSpaceName ? into->tableSpaceName : "";
 		atcmds = lappend(atcmds, atcmd);
 
 		/* storage options */

src/backend/commands/tablecmds.c

@@ -16583,8 +16583,18 @@ ATPrepSetTableSpace(AlteredTableInfo *tab, Relation rel, const char *tablespacen
 {
 	Oid			tablespaceId;
 
-	/* Check that the tablespace exists */
-	tablespaceId = get_tablespace_oid(tablespacename, false);
+	if (tablespacename != NULL && tablespacename[0] == '\0')
+	{
+		/* Use default tablespace if name is empty string */
+		tablespaceId = GetDefaultTablespace(rel->rd_rel->relpersistence, rel->rd_rel->relispartition);
+		if (!OidIsValid(tablespaceId))
+			tablespaceId = MyDatabaseTableSpace;
+	}
+	else
+	{
+		/* Check that the tablespace exists */
+		tablespaceId = get_tablespace_oid(tablespacename, false);
+	}
 
 	/* Check permissions except when moving to database's default */
 	if (OidIsValid(tablespaceId) && tablespaceId != MyDatabaseTableSpace)