| From: | Manfred Koizar <mkoi-pg(at)aon(dot)at> |
|---|---|
| To: | Hannu Krosing <hannu(at)tm(dot)ee> |
| Cc: | thebfh(at)toolsmythe(dot)com, john(at)pagakis(dot)com, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: Performance Concern |
| Date: | 2003-10-27 10:08:49 |
| Message-ID: | 1fqppvc6j3jbj2ifsh2qaagdrtsl52gab8@email.aon.at |
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| Thread: | |
| Lists: | pgsql-performance |
On Sun, 26 Oct 2003 00:13:36 +0300, Hannu Krosing <hannu(at)tm(dot)ee> wrote:
>UPDATE baz
> SET customer_id = '1234'
> WHERE baz_key IN (
> SELECT baz_key
> FROM baz innerbaz
> WHERE customer_id IS NULL
> and innerbaz.baz_key = baz.baz_key
> LIMIT 1000 );
AFAICS this is not what the OP intended. It is equivalent to
UPDATE baz
SET customer_id = '1234'
WHERE customer_id IS NULL;
because the subselect is now correlated to the outer query and is
evaluated for each row of the outer query which makes the LIMIT clause
ineffective.
Servus
Manfred
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