u70b3 commented on code in PR #23684:
URL: https://github.com/apache/datafusion/pull/23684#discussion_r3682343086
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datafusion/sqllogictest/test_files/aggregates_topk.slt:
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@@ -585,3 +587,191 @@ drop table ids;
statement ok
drop table traces;
+
+#######
+# Regression tests for all-NULL groups in TopK aggregation (issues #23440,
#22190):
+# a group whose aggregate inputs are all NULL must be emitted with a NULL
+# aggregate value instead of disappearing from the result
+#######
+statement ok
+CREATE TABLE t0 AS SELECT * FROM (VALUES ('gamma', CAST(NULL AS DOUBLE))) v(s,
y);
+
+# MIN/MAX with NULLS FIRST must use regular aggregation because a group's
+# aggregate can transition from NULL to non-NULL and worsen its rank.
+query TT
+explain select s, max(y) as max_y from t0 group by s order by max_y desc nulls
first limit 3;
+----
+logical_plan
+01)Sort: max_y DESC NULLS FIRST, fetch=3
+02)--Projection: t0.s, max(t0.y) AS max_y
+03)----Aggregate: groupBy=[[t0.s]], aggr=[[max(t0.y)]]
+04)------TableScan: t0 projection=[s, y]
+physical_plan
+01)ProjectionExec: expr=[s@0 as s, max(t0.y)@1 as max_y]
+02)--SortExec: TopK(fetch=3), expr=[max(t0.y)@1 DESC],
preserve_partitioning=[false]
+03)----AggregateExec: mode=SinglePartitioned, gby=[s@0 as s], aggr=[max(t0.y)]
+04)------DataSourceExec: partitions=1, partition_sizes=[1]
+
+# issue #23440: single all-NULL group, MAX DESC NULLS FIRST LIMIT 3
+query R
+SELECT max_y FROM (SELECT s, MAX(y) AS max_y FROM t0 GROUP BY s) ORDER BY
max_y DESC NULLS FIRST LIMIT 3;
+----
+NULL
+
+# issue #22190: single all-NULL group, MIN ASC NULLS LAST LIMIT 20
+query R
+SELECT min_y FROM (SELECT s, MIN(y) AS min_y FROM t0 GROUP BY s) ORDER BY
min_y ASC NULLS LAST LIMIT 20;
Review Comment:
Added a nearby EXPLAIN assertion for the NULLS LAST all-NULL case, verifying
that the physical plan retains AggregateExec with lim=[20]. Thanks!
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