[jira] [Commented] (CALCITE-1906) JdbcSortRule has a bug and it is never chosen

["Julian Hyde (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CALCITE-1906?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16103476#comment-16103476 ] 

Julian Hyde commented on CALCITE-1906:
--------------------------------------

"Never chosen"? I think you mean "not chosen in some circumstances"? If we push down LIMIT and OFFSET then we need to be sure to generate them (in the appropriate dialect) when we generate the SQL. Or is your plan to do the LIMIT and OFFSET outside of the back-end?

It would help if you illustrate with the Calcite query, and the query that you would hope would be pushed down to the back-end.

> JdbcSortRule has a bug and it is never chosen
> ---------------------------------------------
>
>                 Key: CALCITE-1906
>                 URL: https://issues.apache.org/jira/browse/CALCITE-1906
>             Project: Calcite
>          Issue Type: Bug
>          Components: jdbc-adapter
>            Reporter: Luis Fernando Kauer
>            Assignee: Julian Hyde
>
> JdbcSortRule tries to push sort and limit operations to the database.
> Currently offset and limit operations are explicitly not pushed to the database (prevented by the rule) but even sort operations end up not being pushed.
> Checking how other adapters deal with this, like Mongo and Cassandra adapters, I realized that the convert function from JdbcSortRule is different from the others.
> Jdbc-adapter:
> {{
>      if (sort.offset != null || sort.fetch != null) {
>         // Cannot implement "OFFSET n FETCH n" currently.
>         return null;
>       }
>       final RelTraitSet traitSet = sort.getTraitSet().replace(out);
>       return new JdbcSort(rel.getCluster(), traitSet,
>           convert(sort.getInput(), traitSet), sort.getCollation());
> }}
> mongodb-adapter:
> {{
>       final RelTraitSet traitSet =
>           sort.getTraitSet().replace(out)
>               .replace(sort.getCollation());
>       return new MongoSort(rel.getCluster(), traitSet,
>           convert(sort.getInput(), traitSet.replace(RelCollations.EMPTY)),
>           sort.getCollation(), sort.offset, sort.fetch);
> }}
> By fixing JdbcSortRule so that it is just like those others and by removing the code that prevented the rule to match when limit or offset are used seems to solve the problem and JdbcSortRule now is being applied and both sort and limit are being pushed to the database.



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