Consider following SQL: 
 **
 select femail, min(fid) AS main_id, count(fid) AS countids
 from users
 where count(fid) > 1
 group by femail
 **
 Of course, postgreSQL produce error for such wrong statement:
SQL error:
ERROR:  aggregates not allowed in WHERE clause
 I think it would be much better if DBMS will provide us some kind of suggestions, e.g.:
SQL error:
ERROR:  aggregates not allowed in WHERE clause. Consider using HAVING clause.
-- 
Best regards,
Nikolay