Laurent Goujon created CALCITE-2803:
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             Summary: Identify expanded IS NOT DISTINCT FROM expression when 
pushing project past join
                 Key: CALCITE-2803
                 URL: https://issues.apache.org/jira/browse/CALCITE-2803
             Project: Calcite
          Issue Type: Improvement
          Components: core
            Reporter: Laurent Goujon
            Assignee: Julian Hyde


{{IS NOT DISTINCT FROM}} expressions in join condition might actually be 
considered as equi-join conditions, and {{RelOptUtil#splitJoinConditions()}} 
has support for it. But some other join related functions/rules don't.

One of them is {{ProjectJoinTransposeRule}} which tries to push project 
expressions below the join, but ends up modifying the join expression too by 
pushing complex expression below/

For example expression {{OR(AND(IS_NULL($1), IS_NULL($4)), EQUALS($1,$4))}} 
will be changed into {{OR(AND($3, $6), EQUALS($1, $5))}} which makes it 
harder/impossible for {{RelOptUtil#splitJoinConditions()}} to identify an {{IS 
NOT DISTINCT FROM}} equi-join condition.



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