kasakrisz opened a new pull request, #4745:
URL: https://github.com/apache/hive/pull/4745
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### What changes were proposed in this pull request?
Set nullability to of `sum` aggregate function return type based on the
parameter type.
### Why are the changes needed?
Materialized view rewrite algorithm compares all aggregate function return
types in a candidate MV and the query plan about to replace. Nullability is
also checked. Currently if `sum` aggregate function is explicitly defined in a
query (or MV definition) the return type is nullable however if it is
introduced by
[HiveAggregateReduceFunctionsRule](https://github.com/apache/hive/blob/f5d4bf89fb37458a3818d5d5c612b29defb1daa5/ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/rules/HiveAggregateReduceFunctionsRule.java#L326C19-L354)
the return type is always not null due to Hive customization of
[HiveTypeSystemImpl.deriveSumType](https://github.com/apache/hive/blob/f5d4bf89fb37458a3818d5d5c612b29defb1daa5/ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/HiveTypeSystemImpl.java#L174-L187)
The original Calcite version of this function can not be used because it
would always increase the precision of decimal return types to maximum and it
would also decrease the scale in some cases.
Example: the scale would be reduced to 10 in the first column in the
following example
https://github.com/apache/hive/blob/f5d4bf89fb37458a3818d5d5c612b29defb1daa5/ql/src/test/results/clientpositive/llap/decimal_precision.q.out#L603
### Does this PR introduce _any_ user-facing change?
No, but some query's plan may changes.
### Is the change a dependency upgrade?
No.
### How was this patch tested?
```
mvn test -Dtest.output.overwrite -DskipSparkTests
-Dtest=TestMiniLlapLocalCliDriver -Dqfile=materialized_view_create_rewrite_11.q
-pl itests/qtest -Pitests
```
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