diff --git a/parser/parser.y b/parser/parser.y
index 0027cadc05..76acd83168 100644
--- a/parser/parser.y
+++ b/parser/parser.y
@@ -746,23 +746,23 @@ Assignment:
 		if err != nil {
 			yylex.(*lexer).errf("Parse Assignment error: %s", $1.(string))
 		}
-		$$ = *x
+		$$ = x
 	}
 
 AssignmentList:
 	Assignment
 	{
-		$$ = []expression.Assignment{$1.(expression.Assignment)}
+		$$ = []*expression.Assignment{$1.(*expression.Assignment)}
 	}
 |	AssignmentList ',' Assignment
 	{
-		$$ = append($1.([]expression.Assignment), $3.(expression.Assignment))
+		$$ = append($1.([]*expression.Assignment), $3.(*expression.Assignment))
 	}
 
 AssignmentListOpt:
 	/* EMPTY */
 	{
-		$$ = []expression.Assignment{}
+		$$ = []*expression.Assignment{}
 	}
 |	AssignmentList
 
@@ -1727,7 +1727,7 @@ InsertIntoStmt:
 		x.Priority = $2.(int)
 		x.TableIdent = $5.(table.Ident)
 		if $7 != nil {
-			x.OnDuplicate = $7.([]expression.Assignment)
+			x.OnDuplicate = $7.([]*expression.Assignment)
 		}
 		$$ = x
 		if yylex.(*lexer).root {
@@ -4306,7 +4306,7 @@ UpdateStmt:
 		st := &stmts.UpdateStmt{
 			LowPriority:	$2.(bool),
 			TableRefs:	r,
-			List:		$6.([]expression.Assignment),
+			List:		$6.([]*expression.Assignment),
 		}
 		if $7 != nil {
 			st.Where = $7.(expression.Expression)
@@ -4328,7 +4328,7 @@ UpdateStmt:
 		st := &stmts.UpdateStmt{
 			LowPriority:	$2.(bool),
 			TableRefs:	$4.(*rsets.JoinRset),
-			List:		$6.([]expression.Assignment),
+			List:		$6.([]*expression.Assignment),
 			MultipleTable:	true,
 		}
 		if $7 != nil {
diff --git a/stmt/stmts/insert.go b/stmt/stmts/insert.go
index d9096fa372..c32c7fbdcf 100644
--- a/stmt/stmts/insert.go
+++ b/stmt/stmts/insert.go
@@ -60,7 +60,7 @@ type InsertValues struct {
 // See: https://dev.mysql.com/doc/refman/5.7/en/insert.html
 type InsertIntoStmt struct {
 	InsertValues
-	OnDuplicate []expression.Assignment
+	OnDuplicate []*expression.Assignment
 
 	Text string
 }
@@ -335,7 +335,7 @@ func (s *InsertValues) getRow(ctx context.Context, t table.Table, cols []*column
 	return r, nil
 }
 
-func execOnDuplicateUpdate(ctx context.Context, t table.Table, row []interface{}, h int64, cols map[int]expression.Assignment) error {
+func execOnDuplicateUpdate(ctx context.Context, t table.Table, row []interface{}, h int64, cols map[int]*expression.Assignment) error {
 	// On duplicate key update the duplicate row.
 	// Evaluate the updated value.
 	// TODO: report rows affected and last insert id.
@@ -360,8 +360,8 @@ func execOnDuplicateUpdate(ctx context.Context, t table.Table, row []interface{}
 	return nil
 }
 
-func getOnDuplicateUpdateColumns(assignList []expression.Assignment, t table.Table) (map[int]expression.Assignment, error) {
-	m := make(map[int]expression.Assignment, len(assignList))
+func getOnDuplicateUpdateColumns(assignList []*expression.Assignment, t table.Table) (map[int]*expression.Assignment, error) {
+	m := make(map[int]*expression.Assignment, len(assignList))
 
 	for _, v := range assignList {
 		c, err := findColumnByName(t, field.JoinQualifiedName("", v.TableName, v.ColName))
diff --git a/stmt/stmts/update.go b/stmt/stmts/update.go
index abfd0544e4..56e92484f3 100644
--- a/stmt/stmts/update.go
+++ b/stmt/stmts/update.go
@@ -44,7 +44,7 @@ var _ stmt.Statement = (*UpdateStmt)(nil)
 // See: https://dev.mysql.com/doc/refman/5.7/en/update.html
 type UpdateStmt struct {
 	TableRefs     *rsets.JoinRset
-	List          []expression.Assignment
+	List          []*expression.Assignment
 	Where         expression.Expression
 	Order         *rsets.OrderByRset
 	Limit         *rsets.LimitRset
@@ -96,8 +96,8 @@ func findColumnByName(t table.Table, name string) (*column.Col, error) {
 	return c, nil
 }
 
-func getUpdateColumns(assignList []expression.Assignment, fields []*field.ResultField) (map[int]expression.Assignment, error) {
-	m := make(map[int]expression.Assignment, len(assignList))
+func getUpdateColumns(assignList []*expression.Assignment, fields []*field.ResultField) (map[int]*expression.Assignment, error) {
+	m := make(map[int]*expression.Assignment, len(assignList))
 
 	for _, v := range assignList {
 		name := v.ColName
@@ -119,7 +119,7 @@ func getUpdateColumns(assignList []expression.Assignment, fields []*field.Result
 }
 
 func updateRecord(ctx context.Context, h int64, data []interface{}, t table.Table,
-	updateColumns map[int]expression.Assignment, m map[interface{}]interface{},
+	updateColumns map[int]*expression.Assignment, m map[interface{}]interface{},
 	offset int, onDuplicateUpdate bool) error {
 	if err := t.LockRow(ctx, h, true); err != nil {
 		return errors.Trace(err)