Github user adrian-wang commented on the pull request:
https://github.com/apache/spark/pull/837#issuecomment-44923039
Hi Michael, when I was adding the Scala doc, I realized that if the join is
not calculated in LeftSemiJoinHash, then it simply means there's no join keys
for the left semi join. Then if I pushed down those predicates and
conditions(all of them can be pushed down), I only need to verify the if right
table size is null here, to decide whether to output the left table. So
LeftSemiJoinBNL would be very much excessive. Am I right?
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