Re: IN vs =

From: "Lukas" <lukas(at)fmf(dot)vtu(dot)lt>
To: pgsql-novice(at)postgresql(dot)org
Cc: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Subject: Re: IN vs =
Date: 2009-01-27 10:10:34
Message-ID: 19249.217.117.29.29.1233051034.squirrel@fmf.vgtu.lt
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>> 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?

No, it was done on the same database (and same DBMS).

>> 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.

Yes, we found the solution as shown, the question is why it is happening so?
And also, what this patch does? changes the way how operator IN works?

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

Please comment it more - what is wrong with this join? (maybe you mean
that it has to many joins in one query? Also, what do you mean by
"refactor"?

--
Lukas
UAB nSoft
http://www.nsoft.lt
Lukas at nsoft.lt
+370 655 10 655

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