Re: sunquery and estimated rows

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От Tom Lane
Тема Re: sunquery and estimated rows
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Msg-id 13910.1082341013@sss.pgh.pa.us
обсуждение исходный текст
Ответ на sunquery and estimated rows  (Litao Wu <litaowu@yahoo.com>)
Список pgsql-performance
Rod Taylor <rbt@rbt.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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