From: Raphael Bauduin <rblists@gmail.com>
To: pgsql-sql@postgresql.org
Subject: exists and is not null equivalence in query
Date: Thu, 28 May 2009 14:36:31 +0200
Message-ID: <f5227160905280536u4f131850pad984218b0fe8b5@mail.gmail.com> (raw)
Hi,
In some code I am taking over, I found this query:
select count(t.trame_id) as count, v.voiture_num as voitureNum from
arch_trames t left join voiture v on (v.tag_id=t.tag_id)
where
(t.recept_time >= 1243509320691)
and exists (select v2.voiture_num from voiture v2 where v2.tag_id=v.tag_id)
group by v.voiture_num order by v.voiture_num
Am I right that I can replace the "and exists..." clause by
"and v.voiture_num is not null " in this case?
Thanks
Raphaël
--
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Subject: Re: exists and is not null equivalence in query
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