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https://issues.apache.org/jira/browse/CALCITE-4702?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17396817#comment-17396817
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Julian Hyde commented on CALCITE-4702:
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I think that {{transformGroupKeys}} is a little too indirect. One can imagine a
dialect that needs to perform two different transformations on group keys, for
different reasons. The logic would become complicated, because the logic
wouldn't compose.
I suggest {{boolean allowsGroupByConstant}}, with a reasonable definition of
'constant', and a rewrite strategy that works for all affected dialects. It is
mainly dialects in the PostgreSQL family are affected by this behavior, so the
definition of constant and the remedy should be the same for all of them.
(MSSQL may also be affected - please check.)
By the way, I just became aware that Oracle, DB2 and MSSQL have non-standard
behavior for "GROUP BY ()". I have logged CALCITE-4723.
> Error when executing query with GROUP BY constant via JDBC adapter
> ------------------------------------------------------------------
>
> Key: CALCITE-4702
> URL: https://issues.apache.org/jira/browse/CALCITE-4702
> Project: Calcite
> Issue Type: Bug
> Components: core, jdbc-adapter
> Affects Versions: 1.27.0
> Reporter: Stamatis Zampetakis
> Assignee: Stamatis Zampetakis
> Priority: Major
>
> The following functionally equivalent SQL queries are accepted by Calcite and
> produce a valid plan
> {noformat}
> select avg(salary) from employee group by true
> select avg(salary) from employee group by 'a'
> {noformat}
> but they may fail if they are executed via the JDBC adapter since not all
> DBMS allow grouping by constants expressions. Moreover, what works for one
> may not work for the other.
> +Examples+
> The {{GROUP BY TRUE}} query works in Postgres, and MySQL but fails in
> Redshift with the following exception:
> {noformat}
> com.amazon.redshift.util.RedshiftException: ERROR: non-integer constant in
> GROUP BY
> {noformat}
> The {{GROUP BY 'a'}} query works in MySQL but fails in Postgres with the
> following exception:
> {noformat}
> ERROR: non-integer constant in GROUP BY
> {noformat}
> +Edit:+
> The {{GROUP BY}} constant is similar to {{GROUP BY ()}} "nothing" but as
> shown in the discussion below they are not equivalent. There is a nice [blog
> post|https://blog.jooq.org/2018/05/25/how-to-group-by-nothing-in-sql/]
> listing some limitations of various DBMS when it comes to {{GROUP BY ()}}.
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