[SPARK-27514][SQL] Skip collapsing windows with empty window expressions #538
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mccheah
approved these changes
Apr 18, 2019
mccheah
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Upstream SPARK-XXXXX ticket and PR link (if not applicable, explain)
github: apache#24411
jira: https://issues.apache.org/jira/browse/SPARK-27514
What changes were proposed in this pull request?
A previous change moved the removal of empty window expressions to the RemoveNoopOperations rule, which comes after the CollapseWindow rule. Therefore, by the time we get to CollapseWindow, we aren't guaranteed that empty windows have been removed. This change checks that the window expressions are not empty, and only collapses the windows if both windows are non-empty.
A lengthier description and repro steps here: https://issues.apache.org/jira/browse/SPARK-27514
How was this patch tested?
A unit test, plus I reran the breaking case mentioned in the Jira ticket.