sql: fix record-returning udfs with no result

Previously, record-returning UDFs whose last SQL statement returned no
result (i.e., not a SELECT or RETURNING statement) would succeed. They
now return a return type mismatch error, as expected.

Epic: CRDB-19255
Informs: #87289

Release note: None

pkg/sql/logictest/testdata/logic_test/udf_insert

@@ -1,8 +1,8 @@
 statement ok
 CREATE TABLE t (a INT PRIMARY KEY, b INT DEFAULT 0);
 
-statement ok
-CREATE FUNCTION f_should_err() RETURNS RECORD AS
+statement error pq: return type mismatch in function declared to return record\nDETAIL: Function's final statement must be SELECT or INSERT/UPDATE/DELETE RETURNING.
+CREATE FUNCTION f_err() RETURNS RECORD AS
 $$
   INSERT INTO t VALUES (1,2);
 $$ LANGUAGE SQL;

pkg/sql/opt/optbuilder/create_function.go

@@ -239,10 +239,6 @@ func validateReturnType(expected *types.T, cols []scopeColumn) error {
 	if expected.Equivalent(types.Void) {
 		return nil
 	}
-	// If return type is RECORD, any column types are valid.
-	if types.IsRecordType(expected) {
-		return nil
-	}
 
 	if len(cols) == 0 {
 		return pgerror.WithCandidateCode(
@@ -254,6 +250,11 @@ func validateReturnType(expected *types.T, cols []scopeColumn) error {
 		)
 	}
 
+	// If return type is RECORD, any column types are valid.
+	if types.IsRecordType(expected) {
+		return nil
+	}
+
 	if len(cols) == 1 {
 		if !expected.Equivalent(cols[0].typ) &&
 			!cast.ValidCast(cols[0].typ, expected, cast.ContextAssignment) {