X-Original-To: pgsql-sql-postgresql.org@localhost.postgresql.org Received: from localhost (unknown [200.46.204.144]) by svr1.postgresql.org (Postfix) with ESMTP id 4922D5295C for ; Thu, 23 Jun 2005 16:29:02 -0300 (ADT) Received: from svr1.postgresql.org ([200.46.204.71]) by localhost (av.hub.org [200.46.204.144]) (amavisd-new, port 10024) with ESMTP id 15189-09 for ; Thu, 23 Jun 2005 19:28:56 +0000 (GMT) Received: from sss.pgh.pa.us (sss.pgh.pa.us [66.207.139.130]) by svr1.postgresql.org (Postfix) with ESMTP id CFE32528BB for ; Thu, 23 Jun 2005 16:28:52 -0300 (ADT) Received: from sss2.sss.pgh.pa.us (tgl@localhost [127.0.0.1]) by sss.pgh.pa.us (8.13.1/8.13.1) with ESMTP id j5NJSoA6007744; Thu, 23 Jun 2005 15:28:50 -0400 (EDT) To: Markus Bertheau Cc: pgsql-sql@postgresql.org Subject: Re: optimizer, view, union In-reply-to: <1119547917.7430.12.camel@localhost.localdomain> References: <1119547917.7430.12.camel@localhost.localdomain> Comments: In-reply-to Markus Bertheau message dated "Thu, 23 Jun 2005 19:31:57 +0200" Date: Thu, 23 Jun 2005 15:28:50 -0400 Message-ID: <7743.1119554930@sss.pgh.pa.us> From: Tom Lane X-Virus-Scanned: by amavisd-new at hub.org X-Spam-Status: No, hits=0.006 tagged_above=0 required=5 tests=AWL X-Spam-Level: X-Archive-Number: 200506/283 X-Sequence-Number: 21884 Markus Bertheau writes: > Can pg transform > SELECT * FROM ( > SELECT 'foo' AS class, id FROM foo > UNION ALL > SELECT 'bar' AS class, id FROM bar > ) AS a WHERE class = 'foo' [ experiments... ] Yes, if you spell it like this: regression=# explain SELECT * FROM ( regression(# SELECT 'foo'::text AS class, id FROM foo regression(# UNION ALL regression(# SELECT 'bar'::text AS class, id FROM bar regression(# ) AS a WHERE class = 'foo'; QUERY PLAN ------------------------------------------------------------------------- Append (cost=0.00..105.60 rows=4280 width=4) -> Subquery Scan "*SELECT* 1" (cost=0.00..52.80 rows=2140 width=4) -> Seq Scan on foo (cost=0.00..31.40 rows=2140 width=4) -> Subquery Scan "*SELECT* 2" (cost=0.00..52.80 rows=2140 width=4) -> Result (cost=0.00..31.40 rows=2140 width=4) One-Time Filter: false -> Seq Scan on bar (cost=0.00..31.40 rows=2140 width=4) (7 rows) If unadorned, the literals get caught up in some type-conversion issues. (You don't really want them in the output of a view anyway; "unknown" type columns are bad news.) regards, tom lane