Alex Behm has uploaded a new patch set (#6).

Change subject: IMPALA-5016: Simplify COALESCE() in SimplifyConditionalsRule.
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IMPALA-5016: Simplify COALESCE() in SimplifyConditionalsRule.

Simplify COALESCE by skipping leading nulls and applying the following
transformations:
COALESCE(null, a, b) -> COALESCE(a, b);
COALESCE(<literal>, a, b) -> <literal>, when literal is not NullLiteral;
COALESCE(<partition-slotref>, a, b) -> <partition-slotref>,
when the partition column does not contain NULL.

Testing:
added unit tests in ExprRewriteRulesTest

Change-Id: I0325a9e437261b15313bbdf2f22d83376a84b575
---
M fe/src/main/java/org/apache/impala/rewrite/SimplifyConditionalsRule.java
M fe/src/test/java/org/apache/impala/analysis/ExprRewriteRulesTest.java
2 files changed, 126 insertions(+), 17 deletions(-)


  git pull ssh://gerrit.cloudera.org:29418/Impala-ASF refs/changes/15/7015/6
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Gerrit-MessageType: newpatchset
Gerrit-Change-Id: I0325a9e437261b15313bbdf2f22d83376a84b575
Gerrit-PatchSet: 6
Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-Owner: yu feng <[email protected]>
Gerrit-Reviewer: Alex Behm <[email protected]>
Gerrit-Reviewer: yu feng <[email protected]>

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