FrankChen021 commented on code in PR #20093:
URL: https://github.com/apache/druid/pull/20093#discussion_r3821775061
##########
sql/src/main/java/org/apache/druid/sql/calcite/rule/DruidAggregateCaseToFilterRule.java:
##########
@@ -303,9 +303,13 @@ && isIntLiteral(arg2, BigDecimal.ZERO))) {
newProjects.add(arg1);
newProjects.add(filter);
- RelDataType newType =
typeFactory.createTypeWithNullability(call.getType(), true);
+ // Use SUM0 instead of SUM to return 0 instead of NULL when filter
never matches.
+ // This fixes the known inconsistency documented in the class javadoc
where
+ // SUM(CASE WHEN COND THEN COL1 ELSE 0 END) would return NULL instead
of 0
+ // when no rows match the condition.
+ RelDataType newType =
typeFactory.createTypeWithNullability(call.getType(), false);
return AggregateCall.create(
- call.getAggregation(),
+ SqlStdOperatorTable.SUM0,
Review Comment:
[P1] SUM0 still executes as nullable SUM
SumZeroSqlAggregator inherits SumSqlAggregator's nullable native
Long/Float/DoubleSumAggregatorFactory. With no matching filter rows, the
nullable wrapper returns NULL, so native Druid queries still produce NULL for
the empty/no-match cases changed to 0 in filtered_sum.iq.
##########
sql/src/main/java/org/apache/druid/sql/calcite/rule/DruidAggregateCaseToFilterRule.java:
##########
@@ -303,9 +303,13 @@ && isIntLiteral(arg2, BigDecimal.ZERO))) {
newProjects.add(arg1);
newProjects.add(filter);
- RelDataType newType =
typeFactory.createTypeWithNullability(call.getType(), true);
+ // Use SUM0 instead of SUM to return 0 instead of NULL when filter
never matches.
+ // This fixes the known inconsistency documented in the class javadoc
where
+ // SUM(CASE WHEN COND THEN COL1 ELSE 0 END) would return NULL instead
of 0
+ // when no rows match the condition.
+ RelDataType newType =
typeFactory.createTypeWithNullability(call.getType(), false);
return AggregateCall.create(
- call.getAggregation(),
+ SqlStdOperatorTable.SUM0,
Review Comment:
[P2] Rewrite changes all-null semantics
When every row matches the condition and the value is NULL, SUM(CASE WHEN
condition THEN value ELSE 0 END) returns NULL, while SUM0(value) FILTER returns
0. The rewrite applies this universally; the rewrite-disabled test still
documents NULL for the 7=7,null case.
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