Re: IN vs =

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Lukas" <lukas(at)fmf(dot)vtu(dot)lt>
Cc: pgsql-novice(at)postgresql(dot)org
Subject: Re: IN vs =
Date: 2009-01-26 21:33:25
Message-ID: 29955.1233005605@sss.pgh.pa.us
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"Lukas" <lukas(at)fmf(dot)vtu(dot)lt> writes:
> I would like to ask, what is the main difference between operators IN and
> '='.
> Then I use operator IN in JOIN it gives me much worse time (in my example
> ~3000ms) at the same time '=' gives 30ms!
> But the most interesting think is that at the begging (when DB was
> smaller) worked at the same speed as '=', why?

Was it also on a different PG release back then?

> LEFT JOIN b_mokejimu_sudengimai ON (mok_id IN (ms_mokejimas, ms_padengimas))

> Join Filter: (b_mokejimai.mok_id = ANY
> (ARRAY[b_mokejimu_sudengimai.ms_mokejimas,
> b_mokejimu_sudengimai.ms_padengimas]))

The latest 8.2.x and 8.3.x releases contain a patch that avoids using
this construct when there are variables on the right-hand side; I think
that's your problem.

(FWIW, most people would probably say that having to write a join like
this suggests you need to refactor your database structure...)

regards, tom lane

In response to

  • IN vs = at 2009-01-26 20:48:08 from Lukas

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