sql: fix UDF with VOID return type

Functions with VOID returns types should be allowed to produce any
number of columns of any type from their last statement. Prior to this
commit, a calling UDF with a VOID return type would error if the last
statement in the UDF did not produce a value of type VOID. This commit
fixes this minor bug.

Fixes cockroachdb#108297

Release note (bug fix): The last SQL statement in a user-defined
function with a VOID return type can now produce any number of columns
of any type. This bug was present since UDFs were introduced in version
22.2.

Author: mgartner

pkg/sql/logictest/testdata/logic_test/udf_regressions

@@ -580,3 +580,48 @@ statement error pgcode 22P02 invalid input value for enum e105259: "foo"
 SELECT f()
 
 subtest end
+
+
+# Regression test for #108297. UDFs with VOID return types should succeed when
+# the last statement returns columns of any type.
+subtest regression_108297
+
+statement ok
+CREATE OR REPLACE FUNCTION f108297() RETURNS VOID LANGUAGE SQL AS 'SELECT 1'
+
+query T
+SELECT f108297()
+----
+NULL
+
+statement ok
+CREATE OR REPLACE FUNCTION f108297() RETURNS VOID LANGUAGE SQL AS $$
+  SELECT 1, 'foo', NULL
+$$
+
+query T
+SELECT f108297()
+----
+NULL
+
+statement ok
+CREATE SEQUENCE s108297
+
+statement ok
+CREATE OR REPLACE FUNCTION f108297() RETURNS VOID LANGUAGE SQL AS $$
+  SELECT nextval('s108297')
+$$
+
+query T
+SELECT f108297()
+----
+NULL
+
+# Invoking the UDF above should have increment s108297 to 1, so calling nextval
+# again should yield 2.
+query I
+SELECT nextval('s108297')
+----
+2
+
+subtest end

pkg/sql/opt/optbuilder/scalar.go

@@ -24,6 +24,7 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/sql/opt/props"
 	"github.com/cockroachdb/cockroach/pkg/sql/opt/props/physical"
 	"github.com/cockroachdb/cockroach/pkg/sql/parser"
+	"github.com/cockroachdb/cockroach/pkg/sql/parser/statements"
 	"github.com/cockroachdb/cockroach/pkg/sql/pgwire/pgcode"
 	"github.com/cockroachdb/cockroach/pkg/sql/pgwire/pgerror"
 	plpgsql "github.com/cockroachdb/cockroach/pkg/sql/plpgsql/parser"
@@ -728,6 +729,21 @@ func (b *Builder) buildUDF(
 		if err != nil {
 			panic(err)
 		}
+		// Add a VALUES (NULL) statement if the return type of the function is
+		// VOID. We cant simply project NULL from the last statement because all
+		// column would be pruned and the contents of last statement would not
+		// be executed.
+		// TODO(mgartner): This will add some planning overhead for every
+		// invocation of the function. Is there a more efficient way to do this?
+		if rtyp.Family() == types.VoidFamily {
+			stmts = append(stmts, statements.Statement[tree.Statement]{
+				AST: &tree.Select{
+					Select: &tree.ValuesClause{
+						Rows: []tree.Exprs{{tree.DNull}},
+					},
+				},
+			})
+		}
 		body = make([]memo.RelExpr, len(stmts))
 		bodyProps = make([]*physical.Required, len(stmts))
 
@@ -750,6 +766,8 @@ func (b *Builder) buildUDF(
 		if err != nil {
 			panic(err)
 		}
+		// TODO(#108298): Figure out how to handle PLpgSQL functions with VOID
+		// return types.
 		var plBuilder plpgsqlBuilder
 		plBuilder.init(b, colRefs, o.Types.(tree.ParamTypes), stmt.AST, rtyp)
 		stmtScope := plBuilder.build(stmt.AST, bodyScope)

pkg/sql/opt/optbuilder/testdata/udf

@@ -1031,6 +1031,47 @@ project
                                └── variable: s:2
 
 
+# --------------------------------------------------
+# UDFs with VOID return type.
+# --------------------------------------------------
+
+exec-ddl
+CREATE FUNCTION retvoid(i INT) RETURNS VOID LANGUAGE SQL AS 'SELECT i'
+----
+
+build format=show-scalars
+SELECT retvoid(1)
+----
+project
+ ├── columns: retvoid:5
+ ├── values
+ │    └── tuple
+ └── projections
+      └── udf: retvoid [as=retvoid:5]
+           ├── args
+           │    └── const: 1
+           ├── params: i:1
+           └── body
+                ├── project
+                │    ├── columns: i:2
+                │    ├── values
+                │    │    └── tuple
+                │    └── projections
+                │         └── variable: i:1 [as=i:2]
+                └── project
+                     ├── columns: column4:4
+                     ├── limit
+                     │    ├── columns: column1:3
+                     │    ├── values
+                     │    │    ├── columns: column1:3
+                     │    │    └── tuple
+                     │    │         └── null
+                     │    └── const: 1
+                     └── projections
+                          └── assignment-cast: VOID [as=column4:4]
+                               └── variable: column1:3
+
+
 # --------------------------------------------------
 # UDFs that are STRICT/RETURNS NULL ON NULL INPUT.
 # --------------------------------------------------
@@ -1699,11 +1740,11 @@ build set=enable_multiple_modifications_of_table=true
 SELECT upd_ups(1, 2, 3)
 ----
 project
- ├── columns: upd_ups:27
+ ├── columns: upd_ups:29
  ├── values
  │    └── ()
  └── projections
-      └── upd_ups(1, 2, 3) [as=upd_ups:27]
+      └── upd_ups(1, 2, 3) [as=upd_ups:29]
 
 exec-ddl
 CREATE FUNCTION ups2(a1 INT, b1 INT, c1 INT, a2 INT, b2 INT, c2 INT) RETURNS BOOL LANGUAGE SQL AS $$