"Jim C. Nasby" <[EMAIL PROTECTED]> writes:
> On Fri, Aug 04, 2006 at 02:40:30PM -0400, Tom Lane wrote:
>> I would argue that turning on constraint_exclusion ought to instruct
>> the planner to catch this sort of thing, whereas when it's off we
>> ought not expend the cycles.  I have a preliminary patch (below)
>> that seems to fix it.

> How many cycles are we talking about here? Is it even worth the GUC?

I think so.  On simple queries the optimization will *never* fire,
and there's no point in doing the search.  People who are running
complex queries will want to turn it on, but the mysql-equivalent
crew will just find it a waste of cycles.

                        regards, tom lane

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TIP 9: In versions below 8.0, the planner will ignore your desire to
       choose an index scan if your joining column's datatypes do not
       match

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