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https://issues.apache.org/jira/browse/CALCITE-4726?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17400240#comment-17400240
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Julian Hyde edited comment on CALCITE-4726 at 9/3/21, 1:05 AM:
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{quote}The unique semantics of {{COUNT(*)}}
{quote}
There's no other zero-argument aggregate function, but there could be.
CALCITE-4763 proposes adding an aggregate function {{EXISTS_AGG(*)}} that
returns {{FALSE}} if there are zero rows, and {{TRUE}} if there are one or more
rows.
{{EXISTS_AGG(*)}} is always equivalent to {{COUNT(*) > 0}} but it's possible
that it can be implemented more efficiently.
{{EXISTS_AGG}} would have similar semantics to {{COUNT}}, in that its null
behavior is moot because it has no arguments.
Related: {{TRUE_AGG}}, a proposed aggregate function that always returns
{{TRUE}} (CALCITE-4334).
was (Author: julianhyde):
{quote}The unique semantics of {{COUNT\(*)}}{quote}
There's no other zero-argument aggregate function, but there could be. I
considered adding an aggregate function {{EXISTS\(\*)}} (or some other name)
that returns {{FALSE}} if there are zero rows, and {{TRUE}} if there are one or
more rows.
{{EXISTS\(\*)}} is always equivalent to {{COUNT\(\*) > 0}} but it's possible
that it can be implemented more efficiently.
{{EXISTS\(\*)}} would have similar semantics to {{COUNT\(\*)}}, in that its
null behavior is moot because it has no arguments.
Related: {{TRUE_AGG}}, a proposed aggregate function that always returns
{{TRUE}} (CALCITE-4334).
> Add support for filters in AggregateExpandWithinDistinctRule
> ------------------------------------------------------------
>
> Key: CALCITE-4726
> URL: https://issues.apache.org/jira/browse/CALCITE-4726
> Project: Calcite
> Issue Type: Improvement
> Reporter: Will Noble
> Assignee: Will Noble
> Priority: Blocker
>
> Currently, {{AggregateExpandWithinDistinctRule}} does not fire if any of the
> aggregate calls in the aggregate have a filter. We should support filters.
> For example, the following query will not be handled by the current rule due
> to the {{FILTER}} clause:
> {code:java}
> SELECT deptno,
> SUM(sal),
> SUM(sal) WITHIN DISTINCT (job) FILTER (WHERE ename LIKE 'A%')
> FROM emp
> GROUP BY deptno
> {code}
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