Re: Optimizer + bind variables

David Kerr wrote:
> On Wed, Nov 04, 2009 at 07:43:16AM +0800, Craig Ringer wrote:
> - David Kerr wrote:
> - > Does/is it possible for the PG optimizer come up with differnet plans when
> - > you're using bind variables vs when you send static values?
> -
> - Yes, if the bind variable form causes your DB access driver to use a
> - server-side prepared statement. Pg can't use its statistics to improve
> - its query planning if it doesn't have a value for a parameter when it's
> - building the query plan.
>
> hmm, that's a little unclear to me.
>
> let's assume that the application is using prepare:
>
> Assuming the database hasn't changed, would:
> PREPARE bla1 as SELECT * from users where username = '$1';
> explain execute bla1
>
> give the same output as
> explain select * from users where username = 'dave';
>
> ?

No.

This is explained in the notes here:

http://www.postgresql.org/docs/current/static/sql-prepare.html

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