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Date: Thu, 15 Dec 2005 16:36:11 -0800
From: Daniel John Debrunner <djd@debrunners.com>
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Subject: Re: [jira] Updated: (DERBY-649) Useful indexes not used in UNION
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Satheesh Bandaram wrote:


>>And finally one real dumb question, in
>>PredicateList.pushExpressionsIntoSelect I see where you ensure the
>>predicate is a binary operator and has a column reference, but I can't
>>see where the 'don't push expressions' logic is?
>>
>> 
>>
> 
> By not calling pushExpressionsIntoSelect(), the code doesn't push
> expressions... Where ever I find I currently can't handle the situation,
> calling 'continue' in the loop skips pushing that predicate.

I don't think I was clear enough.

>From what I understand, your patch will push predicates like

 a = ?
 a = 3

but will not push expressions like

 a = (1 + b)
 a = cost(c)
 a = rate()

I don't see where predicates of the first type are distinguished from
those of the second type. I'm sure I'm being dumb and it's staring me in
the face.

In PredicateList.pushExpressionsIntoSelect I do see:

  line 1418 - a comment indicating (to me) that there is logic here to
only push "simple" predicates.
  line 1421 - check to see the predicate is a binary relational node
  line 1425 - check to see the left is a column reference
  line 1431 - see if the column is referenced in where it is being pushed to

but I don't see any code that says the right is "simple" so do push, or
the right is "complex" so don't push.

This is as much for my education on the optimizer as well as trying to
understand the patch completely.

Dan.