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https://issues.apache.org/jira/browse/CALCITE-6492?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17867770#comment-17867770
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Zoltan Haindrich commented on CALCITE-6492:
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the *Optionality* class have the following values
* MANDATORY
* OPTIONAL
* IGNORED
* FORBIDDEN
Option A:
Introduce a separate enum should be introduced instead of reusing *Optionality*
I think for the distinct keyword we may have the following cases:
| is distinct allowed | distinct natively supported | ? |
| no | * | FORBIDDEN |
| yes | no | ALLOWED_WITH_REWRITES |
| yes | yes | NATIVELY_SUPPORTED |
Option B:
Declare two functions one with *MANDATORY* and another with *FORBIDDEN* - and
try to utilize that.
Haven't yet explored this.
Option C:
remove the *checkArgument* call to allow *IGNORED*
[here|https://github.com/apache/calcite/blob/0deab6f7e0cb4ec63eae8b59477d6f0fadfd11e8/core/src/main/java/org/apache/calcite/rel/core/AggregateCall.java#L125]
and consider it a valid setting.
I believe the best would be to do (A)
> 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
> Priority: Major
>
> 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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