From: Ragnar Hafstað <gnari@simnet.is>
To: Andrew Sullivan <ajs@crankycanuck.ca>
Cc: pgsql-sql@postgresql.org
Subject: Re: getting count for a specific querry
Date: Fri, 08 Apr 2005 16:17:45 +0000
Message-ID: <1112977065.7444.30.camel@localhost.localdomain> (raw)
In-Reply-To: <20050408150731.GB27718@phlogiston.dyndns.org>
References: <000001c53c3e$f4f5b730$797ba8c0@jfradkin>
<20050408150731.GB27718@phlogiston.dyndns.org>
On Fri, 2005-04-08 at 11:07 -0400, Andrew Sullivan wrote:
> On Fri, Apr 08, 2005 at 09:29:13AM -0400, Joel Fradkin wrote:
> >
> > Is there a fast way to get the count?
>
> Not really, no. You have to perform a count() to get it, which is
> possibly expensive. One way to do it, though, is to do
>
> SELECT count(*) FROM tablename WHERE condition LIMIT n;
>
> or something like that. Assuming the condition is reasonably limited
> (i.e. it's not going to cost you a fortune to run this), you'll get
> the right number back if the number is < n or else you'll get
> n.
come again ?
test=# select count(*) from a;
count
-------
3
(1 row)
test=# select count(*) from a limit 2;
count
-------
3
(1 row)
the LIMIT clause limits the number of rows returned by the select,
in this case 1 row.
maybe you mean something like:
test=# select count(*) from (select * from a limit 2) as foo;
count
-------
2
(1 row)
gnari
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To: pgsql-sql@postgresql.org
Cc: gnari@simnet.is, ajs@crankycanuck.ca
Subject: Re: getting count for a specific querry
In-Reply-To: <1112977065.7444.30.camel@localhost.localdomain>
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