From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Dennis Haney <davh(at)diku(dot)dk> |
Cc: | pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: IN joining |
Date: | 2004-03-05 21:04:59 |
Message-ID: | 11205.1078520699@sss.pgh.pa.us |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
Dennis Haney <davh(at)diku(dot)dk> writes:
> Consider this example:
> SELECT * FROM a,b WHERE a.id = b.id AND (a.id) IN (SELECT c.id FROM c)
> the possible execution trees are {{a,b}, {c}}, {{a,c},{b}} and the code
> seems to also permit {{b,c},{a}}.
No, it does not --- as you say, that would give wrong answers. That
case is eliminated by the tests following this comment:
* JOIN_IN technique will work if outerrel includes LHS and
* innerrel is exactly RHS; conversely JOIN_REVERSE_IN handles
* RHS/LHS.
*
* JOIN_UNIQUE_OUTER will work if outerrel is exactly RHS;
* conversely JOIN_UNIQUE_INNER will work if innerrel is
* exactly RHS.
Joining {b,c} to {a} does not meet any of those four allowed cases.
regards, tom lane
From | Date | Subject | |
---|---|---|---|
Next Message | Andrew Sullivan | 2004-03-05 21:08:26 | Re: 7.4.2 release notes |
Previous Message | Bruce Momjian | 2004-03-05 20:00:18 | 7.4.2 release notes |