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https://issues.apache.org/jira/browse/CALCITE-6214?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17813884#comment-17813884
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Jiajun Xie commented on CALCITE-6214:
-------------------------------------
Sorry, I misunderstood.
The distinct can be removed if we implement `RelOptTable#isKey` for combined
columns.
> Remove DISTINCT in aggregate function if field is unique
> --------------------------------------------------------
>
> Key: CALCITE-6214
> URL: https://issues.apache.org/jira/browse/CALCITE-6214
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Reporter: Jiajun Xie
> Assignee: Jiajun Xie
> Priority: Minor
> Labels: pull-request-available
>
> For the sql
> {code:java}
> select count(distinct x) cnt
> from(
> select distinct sal x from emp
> ) t {code}
> The distinct that in count can be removed.
> {code:java}
> LogicalAggregate(group=[{}], CNT=[COUNT($0)])
> LogicalAggregate(group=[{0}])
> LogicalProject(X=[$5])
> LogicalTableScan(table=[[CATALOG, SALES, EMP]]) {code}
> But `CoreRules#AGGREGATE_REMOVE` not support it, so there are two DISTINCT.
> {code:java}
> LogicalAggregate(group=[{}], CNT=[COUNT(DISTINCT $0)])
> LogicalAggregate(group=[{0}])
> LogicalProject(X=[$5])
> LogicalTableScan(table=[[CATALOG, SALES, EMP]]) {code}
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