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