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https://issues.apache.org/jira/browse/PIG-4953?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15384396#comment-15384396
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Ryan Blue commented on PIG-4953:
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A comment in the code states, "if the leaf is a unary operator it should be a
FilterFunc in which case we don't try to extract partition filter conditions".
This appears to be a stale comment because it refers to partition filter
conditions (one of the subclasses), but this is being used for push-down
filtering as well. Partition filtering will check {{isSupportedOpType}} that
returns false for all unary expressions, so it is perfectly safe to call
{{checkPushDown}} in the partition filtering case.
> Predicate push-down will not run filters for single unary expressions
> ---------------------------------------------------------------------
>
> Key: PIG-4953
> URL: https://issues.apache.org/jira/browse/PIG-4953
> Project: Pig
> Issue Type: Bug
> Components: impl
> Affects Versions: 0.15.0
> Reporter: Ryan Blue
> Assignee: Ryan Blue
>
> While testing PIG-4940, I noticed that a "is not null" predicate was not
> pushed down, but equality predicates were. The problem is that the
> {{FilterExtractor#visit}} method ignores anything that isn't a
> {{BinaryExpression}}. Pushing down {{UnaryExpression}} filters works if the
> expression is linked in by a binary expression, like "b is not null and c ==
> 'val'".
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