747b0392__5_1___Postgres_OnLine_Journal__Microsoft_SQL_Server_2008
[Feature] Dynamic and action SQL in functions [MySQL 5.1] No, but can in Stored procedures which aren't callable from SELECT statements so more limiting than PostgreSQL [PostgreSQL 8.4] Yes! - you can do really cool things with action functions in SELECT statements [Microsoft SQL Server 2008] 
No - but you can in Stored procedures but you can't call stored procs from SELECT statements so much more limiting than PostgreSQL