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List:       postgresql-sql
Subject:    Re: [SQL] Best way to know if there is a row
From:       Tom Lane <tgl () sss ! pgh ! pa ! us>
Date:       2004-09-28 14:24:16
Message-ID: 14451.1096381456 () sss ! pgh ! pa ! us
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Martin Marques <martin@bugs.unl.edu.ar> writes:
> I need to know if there is at least one row in the relation that comes from a 
> determinated query. Which is the best way to do this:

> (a) Build the query with "SELECT * ..." and after executing the query see if 
> numRows()>0
> (b) Build the query with "SELECT count(*) ...", fetch the row and see if 
> count>0

Either of these implies computing the entire query result set, which is
much more computation than you want.  Instead do
	SELECT * .... LIMIT 1
and then see if you got a row or not.  Aside from not computing useless
rows, the LIMIT will bias the optimizer in favor of fast-start plans.

			regards, tom lane

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