Re: Recursive optimization of IN subqueries

-----Original Message-----
From: pgsql-hackers-owner@postgresql.org [mailto:pgsql-hackers-owner@postgresql.org] On Behalf Of Dennis Haney
Sent: Tuesday, January 27, 2004 14:33
To: simon@2ndquadrant.com
Cc: 'Tom Lane'; pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] Recursive optimization of IN subqueries

Simon Riggs wrote:

Tom Lane writes

In the second place, what the code is doing is dependent on an

understanding

of the semantics of IN; I'm not sure it's applicable to, say,

 WHERE outervar > ANY (SELECT innervar FROM ...)

and it's definitely not applicable to

 WHERE outervar > ALL (SELECT innervar FROM ...)

In particular, the optimization paths that involve unique-ifying the

subselect output and then using it as the outer side of a join would

definitely not work for these sorts of things.

I'm not sure if I've understood you correctly in the section above. Are

you saying that these types of queries don't have a meaningful or

defined response? Or just that they wouldn't be very well optimized as a

result of the unique-ifying code changes? Or have I just mis-read the

thread...

I think Tom is refering to the context of the specific optimization.
The optimization we are discussing does nothing to correlated subqueries, and a uncorrolated subquery with > ALL/ANY is actually a computed constant and not a join.

-- 

Dennis