kumarUjjawal commented on code in PR #26013:
URL: https://github.com/apache/datafusion/pull/26013#discussion_r4332369753
##########
datafusion/optimizer/src/decorrelate.rs:
##########
@@ -664,6 +674,16 @@ impl TreeNodeRewriter for PullUpCorrelatedExpr {
.iter()
.all(|expr| partitions_by_all(expr,
&local_correlated_cols))
{
+ // `inner.y = outer.k` keeps the rows of one `y` value for
+ // each outer row, so partitioning by `y` as well gives
each
+ // window function the same rows. A window over an
+ // aggregate with count bug handling stops the pull up in
+ // `pass_through_pulled_up_cols`.
+ if self.can_extend_partition_by {
Review Comment:
`DISTINCT` or a `Filter` between the aggregate and window still drops the
count-bug state, so this guard misses it. I reproduced `(5, NULL)` instead of
`(5, 1)` on `b6debc1c6`; the merge base rejects the query as unsupported. Could
we preserve that state, or stop decorrelation, and add regression tests for
both cases?
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