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Message-ID: <20051025235612.20767.qmail@web54301.mail.yahoo.com>
Date: Tue, 25 Oct 2005 16:56:11 -0700 (PDT)
From: chester c young <chestercyoung@yahoo.com>
Subject: broken join optimization? (8.0)
To: pgsql-sql@postgresql.org
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Transfer-Encoding: 8bit

in php (for example) it's frequently nice to get the structure of a
table without any data, ie, pull a single row with each attribute's
value is null.  I use the query (dual is a table of one row ala
Oracle):

select m.* from dual
left join mytable m on( false );

this works every time, but if mytable is big, then takes a long time. 
needed to rewrite the query to:

select m.* from dual
left join (select * from mytable limit 1) m on( false );

this works as it should - pulls empty row but fast.

it seems to me that a full table scan should not be necessary if the
join condition is false.


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