On Thu, 1 Aug 2002, Tom Lane wrote: > But that isn't an "equivalent query". You've manually transformed > SELECT * FROM (SELECT something UNION SELECT somethingelse) WHERE foo; > into > (SELECT something WHERE foo) UNION (SELECT somethingelse WHERE foo);
Right. > As has been pointed out repeatedly, it's not entirely obvious whether > this is a valid transformation in the general case. Right. And I agreed that it as soon as you first pointed it out. And still do. But the message I was replying to was a similar union query, and I was thinking that that person might be having a similar initial intuitive reaction, "well, it looks kinda the same." I just wanted to note that you need to check this stuff with explain, rather than blindly assuming you know what's going on. > If you can provide a proof that it's always safe, or that it's safe > under such-and-such conditions, I'll see what I can do about making it > happen. It's on my list of things to do, but not high enough that it's likely I'll ever get to it. :-) BTW, if anybody can think of a way to make a view that really does represent my original query, I'd appreciate a hint. cjs -- Curt Sampson <[EMAIL PROTECTED]> +81 90 7737 2974 http://www.netbsd.org Don't you know, in this new Dark Age, we're all light. --XTC ---------------------------(end of broadcast)--------------------------- TIP 5: Have you checked our extensive FAQ? http://www.postgresql.org/users-lounge/docs/faq.html
