| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Rod Taylor <rbt(at)rbt(dot)ca> |
| Cc: | Markus Bertheau <twanger(at)bluetwanger(dot)de>, Litao Wu <litaowu(at)yahoo(dot)com>, Postgresql Performance <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: sunquery and estimated rows |
| Date: | 2004-04-19 02:16:53 |
| Message-ID: | 13910.1082341013@sss.pgh.pa.us |
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| Lists: | pgsql-performance |
Rod Taylor <rbt(at)rbt(dot)ca> writes:
>> It's the only way to prevent it from simplifying when you don't want it
>> to.
> I'm having a difficult time coming up with a circumstance where that is
> beneficial except when stats are out of whack.
Try trawling the archives --- I recall several cases in which people
were using sub-selects for this purpose.
In any case, I don't see the value of having the planner check to see if
a sub-select is just a trivial arithmetic expression. The cases where
people write that and expect it to be simplified are so few and far
between that I can't believe it'd be a good use of planner cycles.
regards, tom lane
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