Commits on Oct 8, 2019

1. opt: add equality push-down rule and map equalities in AssociateJoin … …

   …rule
   
   This commit adds a new normalization rule to enable pushing variable
   equality conditions such as a.x=b.x through joins.
   
   For example, consider this query:
   
     SELECT * FROM a, b, c WHERE a.x=b.x AND a.x=c.x
   
   Given join ordering (a join (b join c)), it should be possible to infer the
   filter b.x=c.x and push it down from the top level onto the join (b join c).
   This commit enables that mapping and pushdown to happen.
   
   In addition, this commit updates the AssociateJoin rule to map as many
   equality conditions as possible to use the output columns of the new inner-most
   join, allowing those conditions to be pushed onto that join.
   
   For example, consider this query:
   
     SELECT * FROM a, b, c WHERE a.x=b.x AND b.x=c.x
   
   If the AssociateJoin rule creates a new join ordering (b join (a join c)),
   it should be possible to map a.x=b.x to a.x=c.x and add it onto the new
   inner-most join (a join c). This commit enables that mapping to happen.
   
   Release note (performance improvement): Improved performance for some join
   queries due to improved filter inference during planning.
   Release justification: This commit will not be merged before the release
   branch is cut.

   

   rytaft committed Oct 8, 2019
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