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https://issues.apache.org/jira/browse/CALCITE-783?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14615991#comment-14615991
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Julian Hyde commented on CALCITE-783:
-------------------------------------
Yes, this is a problem. The "TODO: also monotonic expressions" comment in the
method you patched acknowledges this.
However I wouldn't put the logic into RelMdCollation as you have done. It needs
to be possible to extend the logic when new functions (possibly user-defined)
are added. We have a good start in the SqlOperator method
{code}
public SqlMonotonicity getMonotonicity(
SqlCall call,
SqlValidatorScope scope) {
return SqlMonotonicity.NOT_MONOTONIC;
}
{code}
which is used by the validator and has overrides for functions including
EXTRACT, CAST, FLOOR, SUBSTRING, +, all of which can be monotonic in some
circumstances. SqlValidatorTest.testMonotonic has quite a long list of test
cases. However that method only works on a SqlCall (i.e. a parse tree) whereas
we need to apply the same logic to a RexNode.
So I think the solution is to change the first parameter of that method from
SqlCall to SqlOperatorBinding. SqlCallBinding is an interface which has an
implementation that wraps a SqlCall, and another implementation that wraps a
RexCall.
I have made a start on this in my branch
https://github.com/julianhyde/incubator-calcite/tree/783-monotonicity.
[~milinda], could you finish RelMdCollation.project?
> Project's collation infering logic doesn't handle monotonic expressions
> -----------------------------------------------------------------------
>
> Key: CALCITE-783
> URL: https://issues.apache.org/jira/browse/CALCITE-783
> Project: Calcite
> Issue Type: Bug
> Components: core
> Reporter: Milinda Lakmal Pathirage
> Assignee: Julian Hyde
> Attachments: CALCITE-783-0.patch
>
>
> Current implementation of RelMdCollation#project doesn't handle function
> expressions and because of that we loose any collation metadata related to
> monotonic expressions which can be useful generating streaming query
> execution plans involving tumbling windows.
> Following is how current code looks like (RelMdCollation):
> 185: for (Ord<RexNode> project : Ord.zip(projects)) {
> 186: if (project.e instanceof RexInputRef) {
> 187: targets.put(((RexInputRef) project.e).getIndex(), project.i);
> 188: }
> 189: }
> We only handle projects of type RexInputRef. But to support monotonic
> expressions we should laso handle projects of type RexCall.
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