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https://issues.apache.org/jira/browse/CALCITE-4349?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17262969#comment-17262969
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Julian Hyde commented on CALCITE-4349:
--------------------------------------
I re-created your commit history in
[julianhyde/4349-group-concat|https://github.com/julianhyde/calcite/tree/4349-group-concat].
Review:
* Should be {{allowsSeparator}} not {{allowSeparator}}, to be consistent, and
as I asked
* Add the field in SqlBasicAggFunction, not SqlAggFunction. A new constructor
is unnecessarily disruptive.
* {{stripedCall}} should be {{strippedCall}}
* only strip separator if syntax is ORDERED_FUNCTION
* space after '//'
* '{{i++}}' rather than '{{i += 1}}'
* fix javadoc as I asked previously
* the comment 'group_concat(deptno, ename order by ename separator ';') as
separated_name not supported as list_agg doesn't support it either' is
confusing. It doesn't describe what the test is doing.
> Support GROUP_CONCAT aggregate function for MySQL
> -------------------------------------------------
>
> Key: CALCITE-4349
> URL: https://issues.apache.org/jira/browse/CALCITE-4349
> Project: Calcite
> Issue Type: Bug
> Reporter: Julian Hyde
> Assignee: Zhen Wang
> Priority: Major
> Labels: pull-request-available
> Time Spent: 10m
> Remaining Estimate: 0h
>
> Support the {{GROUP_CONCAT}} aggregate function for MySQL. Here is the
> [syntax|https://dev.mysql.com/doc/refman/8.0/en/aggregate-functions.html#function_group-concat]:
> {noformat}
> GROUP_CONCAT([DISTINCT] expr [,expr ...]
> [ORDER BY {unsigned_integer | col_name | expr}
> [ASC | DESC] [,col_name ...]]
> [SEPARATOR str_val])
> {noformat}
>
> {{GROUP_CONCAT}} is analogous to {{LISTAGG}} (see CALCITE-2754) (and also to
> BigQuery and PostgreSQL's {{STRING_AGG}}, see CALCITE-4335). For example, the
> query
> {code:java}
> SELECT deptno, GROUP_CONCAT(ename ORDER BY empno SEPARATOR ';')
> FROM Emp
> GROUP BY deptno
> {code}
> is equivalent to (and in Calcite's algebra would be desugared to)
> {code:java}
> SELECT deptno, LISTAGG(ename, ';') WITHIN GROUP (ORDER BY empno)
> FROM Emp
> GROUP BY deptno
> {code}
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