[Impala-ASF-CR] IMPALA-5211: Simplifying nullif conditional.

["Philip Zeyliger (Code Review)" <ge...@cloudera.org>]

Hello Matthew Jacobs,

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

    http://gerrit.cloudera.org:8080/7829

to look at the new patch set (#7).

Change subject: IMPALA-5211: Simplifying nullif conditional.
......................................................................

IMPALA-5211: Simplifying nullif conditional.

This commit:
* Converts nullif(x, y) into if(x IS DISTINCT FROM y, x, NULL).
* Re-writes x IS DINSTINCT FROM y -> FALSE if x.equals(y).
* Removes backend implementation of nullif.

As is the case with all conversions, the original nullif(...) is
replaced with if(...) in error messages, explain plans, and so on.

It's important and subtle that the conversion uses "x IS DISTINCT FROM y"
rather than "x != y" so that the simplification can be made while
handling null values correctly. ("x != x" may be either false or null,
but x is distinct from x is always false.)

Testing:
* Added new tests to ExprRewriteRulesTests for nullif and the if(x
  distinct from y, ...) simplification.
* New test for the rewrite in ParserTest.
* Adds an nvl2() test, incidentally.
* Confirmed (using EclEmma, which uses jococo engine) that coverage is good.
* Ran the tests.

Change-Id: Id91ca968a0c0be44e1ec54ad8602f91a5cb2e0e5
---
M be/src/exprs/conditional-functions-ir.cc
M be/src/exprs/conditional-functions.cc
M be/src/exprs/conditional-functions.h
M be/src/exprs/scalar-expr.cc
M be/src/exprs/scalar-expr.h
M common/function-registry/impala_functions.py
M fe/src/main/java/org/apache/impala/analysis/Analyzer.java
M fe/src/main/java/org/apache/impala/analysis/FunctionCallExpr.java
M fe/src/main/java/org/apache/impala/rewrite/BetweenToCompoundRule.java
M fe/src/main/java/org/apache/impala/rewrite/EqualityDisjunctsToInRule.java
M fe/src/main/java/org/apache/impala/rewrite/ExtractCommonConjunctRule.java
M fe/src/main/java/org/apache/impala/rewrite/NormalizeBinaryPredicatesRule.java
M fe/src/main/java/org/apache/impala/rewrite/NormalizeCountStarRule.java
M fe/src/main/java/org/apache/impala/rewrite/NormalizeExprsRule.java
M fe/src/main/java/org/apache/impala/rewrite/SimplifyConditionalsRule.java
A fe/src/main/java/org/apache/impala/rewrite/SimplifyDistinctFromRule.java
M fe/src/test/java/org/apache/impala/analysis/AnalyzeExprsTest.java
M fe/src/test/java/org/apache/impala/analysis/ExprRewriteRulesTest.java
M fe/src/test/java/org/apache/impala/analysis/ParserTest.java
19 files changed, 230 insertions(+), 122 deletions(-)


  git pull ssh://gerrit.cloudera.org:29418/Impala-ASF refs/changes/29/7829/7
-- 
To view, visit http://gerrit.cloudera.org:8080/7829
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Gerrit-MessageType: newpatchset
Gerrit-Change-Id: Id91ca968a0c0be44e1ec54ad8602f91a5cb2e0e5
Gerrit-PatchSet: 7
Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-Owner: Philip Zeyliger <ph...@cloudera.com>
Gerrit-Reviewer: Alex Behm <al...@cloudera.com>
Gerrit-Reviewer: Matthew Jacobs <mj...@cloudera.com>
Gerrit-Reviewer: Philip Zeyliger <ph...@cloudera.com>