Re: Glacially slow nested SELECT - Mailing list pgsql-general

From Tom Lane
Subject Re: Glacially slow nested SELECT
Date
Msg-id 18706.1168886682@sss.pgh.pa.us
Whole thread Raw
In response to Re: Glacially slow nested SELECT  (Demitri Muna <thatsanicehatyouhave@mac.com>)
List pgsql-general
Demitri Muna <thatsanicehatyouhave@mac.com> writes:
> On 15 Jan 2007, at 16:21, Tom Lane wrote:
>> It looks like spview is a view with an embedded ORDER BY?  IIRC that
>> prevents any meaningful optimization of joins to it --- and
>> WHERE-IN-sub-SELECT is a kind of join.

> Thanks for the pointer Tom; removing the ORDER BY from the view did
> the trick. Is there a reason that the sorting can't be done after the
> selection?

Well, it'd require major revisions to the planner, and it'd break
various queries that depend on the planner honoring sub-select ORDER BY
(people use that to guarantee the order in which values are fed to
custom aggregates, for instance).

            regards, tom lane

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