kasakrisz opened a new pull request, #5681:
URL: https://github.com/apache/hive/pull/5681
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### What changes were proposed in this pull request?
Change the parser rule parses case expression like
```
CASE a
WHEN b THEN c
[WHEN d THEN e]* [ELSE f]
END
```
to
```
CASE
WHEN a=b THEN c
[WHEN a=d THEN e]* [ELSE f]
END
```
to build a similar AST like `whenExpression`.
* Remove `GenericUDFCase` because all type of case expressions are handled
by `GenericUDFWhen`
### Why are the changes needed?
When the operand in the case clause has fixed length char type extra
trailing spaces are added to literals in the operands of the when branches. The
current logic always converts the literals in the WHEN branches to the type of
the expression in the CASE clause.
During the AST conversion, type information is lost, and in the second
non-CBO compiler phase, these literals are treated as STRING instead of CHAR.
At execution, the expression in the CASE clause is converted to STRING, and
during this conversion, whitespace characters are trimmed. As a result, the
values are never equal to the literals, leading to data corruption.
### Does this PR introduce _any_ user-facing change?
Yes. Such queries will return correct results.
### Is the change a dependency upgrade?
No
### How was this patch tested?
```
mvn test -Dtest.output.overwrite -Dtest=TestMiniLlapLocalCliDriver
-Dqfile=cbo_case_when_type_conversion.q,cbo_case_when_wrong_type.q -pl
itests/qtest -Pitests
```
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