Adds slt test

Author: Subham Singhal

datafusion/sqllogictest/test_files/propagate_empty_relation_outer_join.slt

@@ -0,0 +1,137 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+
+#   http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+# Test PropagateEmptyRelation rule: outer joins where one side is
+# an EmptyRelation should be replaced with a null-padded projection.
+
+statement ok
+create table t1(a int, b varchar, c double);
+
+statement ok
+create table t2(x int, y varchar, z double);
+
+statement ok
+insert into t1 values (1, 'a', 10.0), (2, 'b', 20.0), (3, 'c', 30.0);
+
+statement ok
+insert into t2 values (1, 'p', 100.0), (2, 'q', 200.0);
+
+statement ok
+set datafusion.explain.logical_plan_only = true;
+
+###
+### LEFT JOIN with empty right (WHERE false subquery)
+###
+
+# The join should be eliminated — no join operator in the plan
+query TT
+explain select * from t1 left join (select * from t2 where false) r on t1.a = r.x;
+----
+logical_plan
+01)Projection: t1.a, t1.b, t1.c, Int32(NULL) AS x, Utf8View(NULL) AS y, Float64(NULL) AS z
+02)--TableScan: t1 projection=[a, b, c]
+
+# Verify result correctness — all left rows with NULLs on right
+query ITRITR rowsort
+select * from t1 left join (select * from t2 where false) r on t1.a = r.x;
+----
+1 a 10 NULL NULL NULL
+2 b 20 NULL NULL NULL
+3 c 30 NULL NULL NULL
+
+###
+### RIGHT JOIN with empty left
+###
+
+query TT
+explain select * from (select * from t1 where false) l right join t2 on l.a = t2.x;
+----
+logical_plan
+01)Projection: Int32(NULL) AS a, Utf8View(NULL) AS b, Float64(NULL) AS c, t2.x, t2.y, t2.z
+02)--TableScan: t2 projection=[x, y, z]
+
+query ITRITR rowsort
+select * from (select * from t1 where false) l right join t2 on l.a = t2.x;
+----
+NULL NULL NULL 1 p 100
+NULL NULL NULL 2 q 200
+
+###
+### FULL JOIN with empty right
+###
+
+query TT
+explain select * from t1 full join (select * from t2 where false) r on t1.a = r.x;
+----
+logical_plan
+01)Projection: t1.a, t1.b, t1.c, Int32(NULL) AS x, Utf8View(NULL) AS y, Float64(NULL) AS z
+02)--TableScan: t1 projection=[a, b, c]
+
+query ITRITR rowsort
+select * from t1 full join (select * from t2 where false) r on t1.a = r.x;
+----
+1 a 10 NULL NULL NULL
+2 b 20 NULL NULL NULL
+3 c 30 NULL NULL NULL
+
+###
+### FULL JOIN with empty left
+###
+
+query TT
+explain select * from (select * from t1 where false) l full join t2 on l.a = t2.x;
+----
+logical_plan
+01)Projection: Int32(NULL) AS a, Utf8View(NULL) AS b, Float64(NULL) AS c, t2.x, t2.y, t2.z
+02)--TableScan: t2 projection=[x, y, z]
+
+query ITRITR rowsort
+select * from (select * from t1 where false) l full join t2 on l.a = t2.x;
+----
+NULL NULL NULL 1 p 100
+NULL NULL NULL 2 q 200
+
+###
+### Filter on top of optimized join
+###
+
+query TT
+explain select * from t1 left join (select * from t2 where false) r on t1.a = r.x where t1.a > 1;
+----
+logical_plan
+01)Projection: t1.a, t1.b, t1.c, Int32(NULL) AS x, Utf8View(NULL) AS y, Float64(NULL) AS z
+02)--Filter: t1.a > Int32(1)
+03)----TableScan: t1 projection=[a, b, c]
+
+query ITRITR rowsort
+select * from t1 left join (select * from t2 where false) r on t1.a = r.x where t1.a > 1;
+----
+2 b 20 NULL NULL NULL
+3 c 30 NULL NULL NULL
+
+###
+### Cleanup
+###
+
+statement ok
+set datafusion.explain.logical_plan_only = false;
+
+statement ok
+drop table t1;
+
+statement ok
+drop table t2;