Zoltan Haindrich created CALCITE-6492:
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Summary: Support aggregate functions which could process DISTINCT
natively
Key: CALCITE-6492
URL: https://issues.apache.org/jira/browse/CALCITE-6492
Project: Calcite
Issue Type: Improvement
Reporter: Zoltan Haindrich
Assignee: Zoltan Haindrich
This could be usefull if the execution engine natively supports some distinct
aggregations natively - there is no rewrite necessary for these functions.
Currently there is support
[SqlAggFunction#getDistinctOptionality|https://github.com/apache/calcite/blob/0deab6f7e0cb4ec63eae8b59477d6f0fadfd11e8/core/src/main/java/org/apache/calcite/sql/SqlAggFunction.java#L187-L189]
- which have overlaps with this - possibly the closest would be to set it to
*IGNORED* if its supported natively...however
* that's a bit misleading as its not IGNORED; but supported...
* there is also
[checkArgument|https://github.com/apache/calcite/blob/0deab6f7e0cb4ec63eae8b59477d6f0fadfd11e8/core/src/main/java/org/apache/calcite/rel/core/AggregateCall.java#L125]
which ensures that *distinct* is not accepted in tht case.
More or less the end result would be to also enhance
AggregateExpandDistinctAggregatesRule with the ability to ignore aggregates.
note: In Druid
* if approximationCountDistinct is disabled ; that [enables a calcite rule
which rewrites *all* disitnct
aggregates|https://github.com/apache/druid/blob/master/sql/src/main/java/org/apache/druid/sql/calcite/planner/CalciteRulesManager.java#L496-L503]
* in the meantime there are also some aggregate functions which support
*distinct* natively like
[string_agg](https://github.com/apache/druid/blob/c9aae9d8e683c0cc9c4687e526b8270f744c57c2/sql/src/main/java/org/apache/druid/sql/calcite/aggregation/builtin/StringSqlAggregator.java#L154)
- which doesn't need any rewrites
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