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The plan generation is heuristic. A SubplanNode is placed as low as possible in the plan tree - as soon as its required parent tuple ids are materialized. This approach is simple to understand and implement, but not always optimal. For example, it may be better to place a Subplan after a selective join, but today we will place it below the join if it is correct to do so. For such scenarios, the straight_join hint can be used to manually tune the join and Subplan order. If straight_join is used, correlated and child table refs are placed into the same SubplanNode if they are adjacent in the FROM clause. Change-Id: I53e4623eb58f8b7ad3d02be15ad8726769f6f8c9 Reviewed-on: http://gerrit.cloudera.org:8080/401 Reviewed-by: Alex Behm <alex.behm@cloudera.com> Tested-by: Internal Jenkins