Re: nested select query take too long - Mailing list pgsql-general

From Stephan Szabo
Subject Re: nested select query take too long
Date
Msg-id 20011119092847.S47208-100000@megazone23.bigpanda.com
Whole thread Raw
In response to nested select query take too long  ("Arsalan Zaidi" <azaidi@directi.com>)
List pgsql-general
On Mon, 19 Nov 2001, Arsalan Zaidi wrote:

> Hi.
>
> The following query takes absolutely *ages* to run. Even with just a 1000
> records in each table. It seems to me that the nested query is being run for
> *every* value in the dom_ns table.
>
> SELECT DISTINCT dom_ns.domname, dom_ns.tldtype FROM dom_ns WHERE
> dom_ns.domname NOT IN (SELECT domname FROM domains WHERE domname IS NOT
> NULL);
>
> Why should is this happening? I just want the nested query to run once!

See the FAQ.  Short form: It'll be faster if you rewrite to use exists
rather than IN.



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