Add slt test which fails without fix

Author: Shiv Bhatia

datafusion/sqllogictest/test_files/push_down_filter_sort_fetch.slt

@@ -0,0 +1,64 @@
+# 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.
+
+# Regression tests: filters must NOT be pushed below Sort with fetch (LIMIT).
+#
+# When a Sort node has a fetch (e.g. ORDER BY ... LIMIT N), pushing a filter
+# below it changes query semantics: the limit should apply before the filter.
+
+statement ok
+CREATE TABLE t(id INT, value INT) AS VALUES
+(1, 100),
+(2, 200),
+(3, 300),
+(4, 400),
+(5, 500);
+
+# Correct result: first take the 3 smallest values (100, 200, 300),
+# then filter value > 200 → only (3, 300).
+#
+# Without the fix the filter is pushed below the sort+limit, producing
+# the 3 smallest values *after* filtering: (300, 400, 500) — wrong.
+query II
+SELECT * FROM (SELECT * FROM t ORDER BY value LIMIT 3) sub WHERE sub.value > 200;
+----
+3 300
+
+# Same test with DESC ordering.
+# First take the 3 largest values (500, 400, 300), then filter value < 400.
+# Correct: (3, 300). Buggy: (1, 100), (2, 200), (3, 300).
+query II
+SELECT * FROM (SELECT * FROM t ORDER BY value DESC LIMIT 3) sub WHERE sub.value < 400;
+----
+3 300
+
+# Verify the EXPLAIN plan keeps the filter above the sort+fetch.
+query TT
+EXPLAIN SELECT * FROM (SELECT * FROM t ORDER BY value LIMIT 3) sub WHERE sub.value > 200;
+----
+logical_plan
+01)SubqueryAlias: sub
+02)--Filter: t.value > Int32(200)
+03)----Sort: t.value ASC NULLS LAST, fetch=3
+04)------TableScan: t projection=[id, value]
+physical_plan
+01)FilterExec: value@1 > 200
+02)--SortExec: TopK(fetch=3), expr=[value@1 ASC NULLS LAST], preserve_partitioning=[false]
+03)----DataSourceExec: partitions=1, partition_sizes=[1]
+
+statement ok
+DROP TABLE t;