On Wed, 21 May 2008 15:09:49 +0200, Richard Huxton <dev@archonet.com>
wrote:
> Luke Lonergan wrote:
>> The problem is that the implied join predicate is not being
>> propagated. This is definitely a planner deficiency.
>
> IIRC only equality conditions are propagated and gt, lt, between aren't.
> I seem to remember that the argument given was that the cost of
> checking for the ability to propagate was too high for the frequency
> when it ocurred.
>
> Of course, what was true for code and machines of 5 years ago might not
> be so today.
>
Suggestion : when executing a one-off sql statement, optimizer should try
to offer "best effort while being fast" ; when making a plan that will be
reused many times (ie PREPARE, functions...) planning time could be
muuuuch longer...