evalengine: TypeOf for Columns should only use value type when we hav…

…e a value (#13148) (#13154)

Signed-off-by: Andres Taylor <[email protected]>

go/vt/vtgate/evalengine/expr_column_test.go

@@ -0,0 +1,63 @@
+/*
+Copyright 2023 The Vitess Authors.
+
+Licensed 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.
+*/
+
+package evalengine
+
+import (
+	"testing"
+
+	"vitess.io/vitess/go/sqltypes"
+	querypb "vitess.io/vitess/go/vt/proto/query"
+)
+
+func TestTypeOf(t *testing.T) {
+	env := &ExpressionEnv{
+		BindVars: make(map[string]*querypb.BindVariable),
+	}
+
+	field1 := &querypb.Field{
+		Name:  "field1",
+		Type:  querypb.Type_INT64,
+		Flags: uint32(querypb.MySqlFlag_NOT_NULL_FLAG),
+	}
+	field2 := &querypb.Field{
+		Name:  "field2",
+		Type:  querypb.Type_VARCHAR,
+		Flags: 0,
+	}
+	fields := []*querypb.Field{field1, field2}
+
+	c := &Column{}
+	env.Row = sqltypes.Row{sqltypes.NewInt64(10)}
+	env.Fields = fields
+
+	t.Run("Check when row value is not null", func(t *testing.T) {
+		typ, f := c.typeof(env)
+		if typ != sqltypes.Int64 || f != flag(0) {
+			t.Errorf("typeof() failed, expected sqltypes.Int64 and typeFlag 0, got %v and %v", typ, f)
+		}
+	})
+
+	t.Run("Check when row value is null", func(t *testing.T) {
+		env.Row = sqltypes.Row{
+			sqltypes.NULL,
+		}
+		typ, flag := c.typeof(env)
+		if typ != querypb.Type_INT64 || flag != flagNullable {
+			t.Errorf("typeof() failed, expected querypb.Type_INT64 and flagNullable, got %v and %v", typ, flag)
+		}
+	})
+}

go/vt/vtgate/evalengine/expressions.go

@@ -578,10 +578,9 @@ func (c *Column) typeof(env *ExpressionEnv) (sqltypes.Type, flag) {
 	// we'll try to do the best possible with the information we have
 	if c.Offset < len(env.Row) {
 		value := env.Row[c.Offset]
-		if value.IsNull() {
-			return sqltypes.Null, flagNull | flagNullable
+		if !value.IsNull() {
+			return value.Type(), flag(0)
 		}
-		return value.Type(), flag(0)
 	}
 
 	if c.Offset < len(env.Fields) {