Fix correlated subquery empty defaults for regr_count and approx_distinct#22319
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Fix correlated subquery empty defaults for regr_count and approx_distinct#22319nathanb9 wants to merge 1 commit into
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Which issue does this PR close?
regr_count,approx_distinctin correlated subquery #22317.Rationale for this change
Correlated scalar subqueries with ungrouped aggregates are decorrelated into joins. For unmatched outer rows, the rewritten join naturally produces NULLs on the right side, so DataFusion has compensation logic for aggregates that should return a non-NULL value on empty input.
That compensation previously special-cased
countby name. As a result, other aggregates with non-NULL empty-input results, such asregr_countandapprox_distinct, incorrectly returned NULL after decorrelation.What changes are included in this PR?
This PR updates decorrelation to use each aggregate UDF's
default_value()instead of hard-codingcount.It also adds empty-input defaults for:
regr_count:UInt64(0)approx_distinct:UInt64(0)Regression coverage is added for correlated scalar subqueries using these aggregates in projection expressions and filters.
Are these changes tested?
Yes.
cargo fmt --all cargo test -p datafusion-sqllogictest --test sqllogictests -- subquery.sltAre there any user-facing changes?
Yes. Queries using
regr_countorapprox_distinctin correlated scalar subqueries now return0for unmatched outer rows instead ofNULL, matching the aggregate behavior on empty input.