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Re: Seq scan with a like operator

From: Peter Eisentraut <peter_e(at)gmx(dot)net>
To: "Jouneau Luc" <Luc(dot)Jouneau(at)diamant(dot)jouy(dot)inra(dot)fr>
Cc: <pgsql-admin(at)postgresql(dot)org>
Subject: Re: Seq scan with a like operator
Date: 2004-07-23 16:00:07
Message-ID: 200407231800.07825.peter_e@gmx.net (view raw or flat)
Thread:
Lists: pgsql-admin
Am Freitag, 23. Juli 2004 17:24 schrieb Jouneau Luc:
> I didn't notice it when I red the doc, but if I create the index as
> specified then it is the query with equal operator which use a seq scan.
> Do I have to create 2 indexes on the same column (with different datatype)
> in order to support different kind of queries ?

Yes.

> Well, It seems quite strange to me :
> Suppose you have an user interface in which user can parameter his query on
> 4 varchar fields (independantly, i.e field 4 does not need to have field
> 1,2 or 3 filled), and you allow to use generic character such as '*' or '?'
> (which will be translated into '%' and '_'). User can also fill in exact
> values.

I think that kind of interface would use the LIKE operator no matter whether 
the user entered wildcards or not.

> It would also mean that support both exact generic queries double the
> indexing task on update/insert/delete.

Well, if you want to optimize lots of different queries, the system needs to 
provide lots of different support.

-- 
Peter Eisentraut
http://developer.postgresql.org/~petere/

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