From: | Mike Mascari <mascarm(at)mascari(dot)com> |
---|---|
To: | Steve Heaven <steve(at)thornet(dot)co(dot)uk> |
Cc: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: Query plan and sub-queries |
Date: | 2000-08-08 12:24:28 |
Message-ID: | 398FFBFC.65E69E05@mascari.com |
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Lists: | pgsql-general pgsql-hackers |
Steve Heaven wrote:
>
> When the WHERE clause includes a sub query the query plan seems to ignore
> indexes.
This is a FAQ:
4.23) Why are my subqueries using IN so slow?
Currently, we join subqueries to outer queries by sequential
scanning the result of the subquery for each row of the outer
query. A workaround is to replace IN with EXISTS:
SELECT *
FROM tab
WHERE col1 IN (SELECT col2 FROM TAB2)
to:
SELECT *
FROM tab
WHERE EXISTS (SELECT col2 FROM TAB2 WHERE col1 = col2)
We hope to fix this limitation in a future release.
Hope that helps,
Mike Mascari
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