rubenada commented on code in PR #4614:
URL: https://github.com/apache/calcite/pull/4614#discussion_r2498621314
##########
core/src/main/java/org/apache/calcite/sql2rel/RelDecorrelator.java:
##########
@@ -804,17 +804,18 @@ protected RexNode removeCorrelationExpr(
}
}
+ final Correlate correlate = frameStack.peek() == null ? null :
frameStack.peek().left;
if (rel.getGroupType() == Aggregate.Group.SIMPLE
&& rel.getGroupSet().isEmpty()
&& !frame.corDefOutputs.isEmpty()
&& (
// If there is a COUNT, we must call rewriteScalarAggregate (to
distinguish 0 vs empty)
hasCount
||
- // Otherwise call only for non-LEFT Correlate, because for LEFT:
NULL is effectively
- // the same as empty (which promotes NULL on the RHS)
+ // Otherwise call except if this is a LEFT Correlate with the
Aggregate being its RHS,
+ // in that case NULL is effectively the same as empty (which
promotes NULL on the RHS)
(!parentPropagatesNullValues
- && requireNonNull(frameStack.peek()).left.getJoinType() !=
JoinRelType.LEFT))) {
Review Comment:
I could also add the "counter-example" as a unit test in
RelDecorrelatorTest, but it would require some minor adjustments in
RelDecorrelator to allow running the decorrelation algorithm without any type
of rule prior. It's manageable, adds more flexibility (and can be done in a way
to keep things backward-compatible)
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