1 files changed, 32 insertions, 0 deletions
diff --git a/src/test/regress/sql/misc_functions.sql b/src/test/regress/sql/misc_functions.sql
index 1a20c1f765..7a71f7659c 100644
--- a/src/test/regress/sql/misc_functions.sql
+++ b/src/test/regress/sql/misc_functions.sql
@@ -29,3 +29,35 @@ SELECT num_nulls(VARIADIC '{}'::int[]);
 -- should fail, one or more arguments is required
 SELECT num_nonnulls();
 SELECT num_nulls();
+
+--
+-- Test adding a support function to a subject function
+--
+
+CREATE FUNCTION my_int_eq(int, int) RETURNS bool
+  LANGUAGE internal STRICT IMMUTABLE PARALLEL SAFE
+  AS $$int4eq$$;
+
+-- By default, planner does not think that's selective
+EXPLAIN (COSTS OFF)
+SELECT * FROM tenk1 a JOIN tenk1 b ON a.unique1 = b.unique1
+WHERE my_int_eq(a.unique2, 42);
+
+-- With support function that knows it's int4eq, we get a different plan
+ALTER FUNCTION my_int_eq(int, int) SUPPORT test_support_func;
+
+EXPLAIN (COSTS OFF)
+SELECT * FROM tenk1 a JOIN tenk1 b ON a.unique1 = b.unique1
+WHERE my_int_eq(a.unique2, 42);
+
+-- Also test non-default rowcount estimate
+CREATE FUNCTION my_gen_series(int, int) RETURNS SETOF integer
+  LANGUAGE internal STRICT IMMUTABLE PARALLEL SAFE
+  AS $$generate_series_int4$$
+  SUPPORT test_support_func;
+
+EXPLAIN (COSTS OFF)
+SELECT * FROM tenk1 a JOIN my_gen_series(1,1000) g ON a.unique1 = g;
+
+EXPLAIN (COSTS OFF)
+SELECT * FROM tenk1 a JOIN my_gen_series(1,10) g ON a.unique1 = g;