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From "Thomas Tauber-Marshall (Code Review)" <>
Subject [Impala-ASF-CR] IMPALA-5725: coalesce() with outer join incorrectly rewritten
Date Wed, 02 Aug 2017 21:49:42 GMT
Hello Matthew Jacobs,

I'd like you to reexamine a change.  Please visit

to look at the new patch set (#2).

Change subject: IMPALA-5725: coalesce() with outer join incorrectly rewritten

IMPALA-5725: coalesce() with outer join incorrectly rewritten

A recent change, IMPALA-5016, added an expr rewrite rule to simplfy
coalesce(). This rule eliminates the coalesce() when its first
parameter (that isn't constant null) is a SlotRef pointing to a
SlotDescriptor that is non-nullable (for example because it is from
a non-nullable Kudu column or because it is from an HDFS partition
column with no null partitions), under the assumption that the SlotRef
could never have a null value.

This assumption is violated when the SlotRef is the output of an
outer join, leading to incorrect results being returned. The problem
is that the nullability of a SlotDescriptor (which determines whether
there is a null indicator bit in the tuple for that slot) is a
slightly different property than the nullability of a SlotRef pointing
to that SlotDescriptor (since the SlotRef can still be NULL if the
entire tuple is NULL).

This patch removes the portion of the rewrite rule that considers
the nullability of the SlotDescriptor. This means that we're missing
out on some optimizations opportunities and we should revisit this in
a way that works with outer joins (IMPALA-5753)

- Updated FE tests.
- Added regression tests to exprs.test

Change-Id: I1ca6df949f9d416ab207016236dbcb5886295337
M fe/src/main/java/org/apache/impala/analysis/
M fe/src/main/java/org/apache/impala/rewrite/
M fe/src/test/java/org/apache/impala/analysis/
M testdata/workloads/functional-query/queries/QueryTest/exprs.test
4 files changed, 29 insertions(+), 44 deletions(-)

  git pull ssh:// refs/changes/67/7567/2
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Gerrit-MessageType: newpatchset
Gerrit-Change-Id: I1ca6df949f9d416ab207016236dbcb5886295337
Gerrit-PatchSet: 2
Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-Owner: Thomas Tauber-Marshall <>
Gerrit-Reviewer: Alex Behm <>
Gerrit-Reviewer: Matthew Jacobs <>

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