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https://issues.apache.org/jira/browse/CALCITE-4702?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17396749#comment-17396749
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Soumyakanti Das commented on CALCITE-4702:
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I think we can introduce a new method in `SqlDialect` like `public
List<SqlNode> transformGroupKeys(List<SqlNode> groupKeys)` which will simply
return the list. And this method can be overridden in `RedshiftSqlDialect`,
etc, to loop over the keys and transform the constant fields. The method
`transformGroupKeys` can be called right after populating the `groupKeys` in
`RelToSqlConverter.generateGroupList`.
If you all agree with the API, I can start working on a PR.
Also, regarding the transformation itself there are two ways we can go about it.
1. Transform GROUP BY <any constant> to GROUP BY (SELECT 1)
2. Transform GROUP BY true -> GROUP BY (SELECT true), GROUP BY 'a' -> GROUP BY
(SELECT 'a'), etc.
Do let me know what your thoughts are regarding these transformations.
> 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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