| From: | John A Meinel <john(at)arbash-meinel(dot)com> |
|---|---|
| To: | Manfred Koizar <mkoi-pg(at)aon(dot)at>, Postgresql Performance <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: Insert performance (OT?) |
| Date: | 2005-08-17 22:02:28 |
| Message-ID: | 4303B3F4.9010306@arbash-meinel.com |
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| Thread: | |
| Lists: | pgsql-performance |
Manfred Koizar wrote:
> On Tue, 19 Jul 2005 11:51:51 +0100, Richard Huxton <dev(at)archonet(dot)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 :-(
Couldn't you use "INTERSECT" then? To only get the rows that *both*
queries return?
John
=:->
>
> Servus
> Manfred
>
>
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