ORCA: keep HAVING above a scalar GbAgg in CNormalizer::FPushable

src/backend/gporca/libgpopt/src/operators/CNormalizer.cpp

@@ -18,6 +18,7 @@
 #include "gpopt/base/CUtils.h"
 #include "gpopt/operators/CLogical.h"
 #include "gpopt/operators/CLogicalConstTableGet.h"
+#include "gpopt/operators/CLogicalGbAgg.h"
 #include "gpopt/operators/CLogicalInnerJoin.h"
 #include "gpopt/operators/CLogicalLeftOuterCorrelatedApply.h"
 #include "gpopt/operators/CLogicalLeftOuterJoin.h"
@@ -126,6 +127,18 @@ CNormalizer::FPushable(CExpression *pexprLogical, CExpression *pexprPred)
 		return false;
 	}
 
+	// do not push predicates below a scalar (plain) aggregate, i.e. one with
+	// no grouping columns. A scalar aggregate produces exactly one output row
+	// regardless of input cardinality, so a predicate above it (HAVING clause)
+	// must be evaluated against that output row, not the aggregate's input.
+	// Pushing e.g. "HAVING false" below would leave the agg emitting one row
+	// (e.g. count = 0) instead of zero rows.
+	if (COperator::EopLogicalGbAgg == pexprLogical->Pop()->Eopid() &&
+		0 == CLogicalGbAgg::PopConvert(pexprLogical->Pop())->Pdrgpcr()->Size())
+	{
+		return false;
+	}
+
 
 	CColRefSet *pcrsUsed = pexprPred->DeriveUsedColumns();
 	CColRefSet *pcrsOutput = pexprLogical->DeriveOutputColumns();

src/test/regress/expected/groupingsets.out

@@ -958,6 +958,25 @@ explain (costs off)
  Optimizer: Postgres query optimizer
 (13 rows)
 
+-- HAVING with constant-false predicate on an empty grouping set must emit
+-- zero rows, not the default scalar-aggregate row.
+select count(*) from gstest2 group by grouping sets (()) having false;
+ count 
+-------
+(0 rows)
+
+explain (costs off)
+  select count(*) from gstest2 group by grouping sets (()) having false;
+             QUERY PLAN
+-------------------------------------
+ Aggregate
+   Group Key: ()
+   Filter: false
+   ->  Result
+         One-Time Filter: false
+ Optimizer: Postgres query optimizer
+(6 rows)
+
 -- HAVING with GROUPING queries
 select ten, grouping(ten) from onek
 group by grouping sets(ten) having grouping(ten) >= 0

src/test/regress/expected/groupingsets_optimizer.out

@@ -975,6 +975,22 @@ explain (costs off)
  Optimizer: GPORCA
 (13 rows)
 
+-- HAVING with constant-false predicate on an empty grouping set must emit
+-- zero rows, not the default scalar-aggregate row.
+select count(*) from gstest2 group by grouping sets (()) having false;
+ count 
+-------
+(0 rows)
+
+explain (costs off)
+  select count(*) from gstest2 group by grouping sets (()) having false;
+        QUERY PLAN
+--------------------------
+ Result
+   One-Time Filter: false
+ Optimizer: GPORCA
+(3 rows)
+
 -- HAVING with GROUPING queries
 select ten, grouping(ten) from onek
 group by grouping sets(ten) having grouping(ten) >= 0

src/test/regress/sql/groupingsets.sql

@@ -353,6 +353,12 @@ explain (costs off)
   select v.c, (select count(*) from gstest2 group by () having v.c)
     from (values (false),(true)) v(c) order by v.c;
 
+-- HAVING with constant-false predicate on an empty grouping set must emit
+-- zero rows, not the default scalar-aggregate row.
+select count(*) from gstest2 group by grouping sets (()) having false;
+explain (costs off)
+  select count(*) from gstest2 group by grouping sets (()) having false;
+
 -- HAVING with GROUPING queries
 select ten, grouping(ten) from onek
 group by grouping sets(ten) having grouping(ten) >= 0