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https://issues.apache.org/jira/browse/CALCITE-2224?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16671980#comment-16671980
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Julian Hyde commented on CALCITE-2224:
--------------------------------------
Sorry I missed this. Thanks for this contribution - it is a very useful
extension to Calcite's SQL. It's a large PR, so of course we want to complete
it in a timely manner, to prevent conflicts. I marked it to fix in 1.18 so that
we don't forget it.
I briefly reviewed and the changes look good:
* I'm glad you have tests for the parser and sql-to-rel converter. Can you also
add validator tests (SqlValidatorTest.java).
* Also add some tests (both sql-to-rel and .iq) where WITHIN GROUP appears on
top of a join.
* Please deprecate the two {{RelBuilder.aggregateCall}} methods that take a
filter but not orderKeys. Also move the {{orderKeys}} argument earlier - it
should be after {{filter}} and before {{alias}}, so that {{operands}} continues
to be last. ({{operands}} has to be last because it is var-args.)
* Update algebra.md due to the changes to RelBuilder
Let me know when it's ready to review again.
> 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
> Fix For: 1.18.0
>
>
> 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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