From: | Peter Eisentraut <peter_e(at)gmx(dot)net> |
---|---|
To: | Rob Prowel <tempest766(at)yahoo(dot)com> |
Cc: | pgsql-bugs(at)postgresql(dot)org |
Subject: | Re: is this a bug or do I not understand the query planner? |
Date: | 2005-11-03 23:59:27 |
Message-ID: | 200511040059.27965.peter_e@gmx.net |
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Thread: | |
Lists: | pgsql-bugs |
Rob Prowel wrote:
> two almost identical queries: one searches for
> read in ('N','n')
> and the other searches for
> read in ('Y','y').
>
> the (explain) SQL statement says that one uses the
> index on the (read) field and the other does a
> sequential table scan. Why!!!???? I can think of no
> logical reason for this behavior.
Imagine a table with one million 'Y' and one 'N'. Searching for the
first should not use an index, searching for the second should. A
similar case probably applies here. I hope that is logical enough for
you. :)
In general, if you disagree with a plan choice, you should provide
evidence that the chosen plan is in practice worse then the one you
would have preferred.
--
Peter Eisentraut
http://developer.postgresql.org/~petere/
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