Horton

Re: Insert performance (OT?)

Manfred Koizar <mkoi-pg@aon.at>

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From: Manfred Koizar <mkoi-pg@aon.at>
To: Richard Huxton <dev@archonet.com>
Cc: Yves Vindevogel <yves.vindevogel@implements.be>, 'Postgresql Performance' <pgsql-performance@postgresql.org>
Date: 2005-08-17T20:25:09Z
Lists: pgsql-performance 
On Tue, 19 Jul 2005 11:51:51 +0100, Richard Huxton <dev@archonet.com>
wrote:
>You could get away with one query if you converted them to left-joins:
>INSERT INTO ...
>SELECT * FROM upload LEFT JOIN ... WHERE f3 IS NULL
>UNION
>SELECT * FROM upload LEFT JOIN ... WHERE f4 IS NULL

For the archives:  This won't work.  Each of the two SELECTs
eliminates rows violating one of the two constraints but includes rows
violating the other constraint.  After the UNION you are back to
violating both constraints :-(

Servus
 Manfred