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https://issues.apache.org/jira/browse/CALCITE-2224?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16416558#comment-16416558
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Julian Hyde commented on CALCITE-2224:
--------------------------------------
I don't plan to work on this. I filed it just as a placeholder for future
discussions. If you would like to work on it (or just some of it) that would be
awesome.
I imagine we would add a {{List<RelFieldCollation>}} field to
{{AggregateCall}}, which would be the empty list most of the time.
> WITHIN GROUP clause for aggregate functions
> -------------------------------------------
>
> Key: CALCITE-2224
> URL: https://issues.apache.org/jira/browse/CALCITE-2224
> Project: Calcite
> Issue Type: Bug
> Reporter: Julian Hyde
> Assignee: Julian Hyde
> Priority: Major
>
> The {{WITHIN GROUP}} clause lets aggregate functions operate on a sorted list
> of rows, rather than the usual unsorted collection. Order only matters for a
> few aggregate functions, but we should allow it for all.
> Other analytic functions where {{WITHIN GROUP}} would have an effect:
> {{RANK}}, {{PERCENT_RANK}}, {{FIRST_VALUE}}, {{LAST_VALUE}},
> {{PERCENTILE_CONT}}, {{PERCENTILE_DISC}}.
> {{LISTAGG(value [, separator])}} is an [Oracle
> function|https://docs.oracle.com/cloud/latest/db112/SQLRF/functions089.htm#SQLRF30030]
> that concatenates strings. E.g.
> {code:java}
> SELECT LISTAGG(last_name, '; ')
> WITHIN GROUP (ORDER BY hire_date, last_name)
> FROM Emp
> GROUP BY deptno{code}
> {{STRING_AGG(value [, separator])}} is a [Microsoft SQL Server function|]
> that does something similar.
> {{GROUP_CONCAT(value [, separator] [ORDER BY expr [, expr]...)}} is the
> [MySQL|https://dev.mysql.com/doc/refman/5.7/en/group-by-functions.html#function_group-concat]
> equivalent to {{LISTAGG}}. Note the optional {{ORDER BY}} clause within the
> parentheses.
> {{COLLECT(value)}} is a SQL standard aggregate function that creates
> multisets. Oracle added a non-standard {{ORDER BY}} clause within the
> parentheses.
> In my opinion, {{WITHIN GROUP}} should always be optional. {{LISTAGG}}
> without {{WITHIN GROUP}} would produce non-deterministic output (which is
> OK); other aggregate functions such as {{MIN}} and {{SUM}} would just ignore
> {{WITHIN GROUP}}.
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