diff --git a/mysql/type.go b/mysql/type.go
index 36f3441a94b7f..9baad459e1c59 100644
--- a/mysql/type.go
+++ b/mysql/type.go
@@ -48,6 +48,10 @@ const (
 	TypeGeometry
 )
 
+// UnInitializedType is an uninitialized type code.
+// TypeDecimal is the old type code for decimal and not be used in the new mysql version.
+const UnInitializedType = TypeDecimal
+
 // Flag informations.
 const (
 	NotNullFlag     = 1   /* Field can't be NULL */
diff --git a/plan/plans/fields.go b/plan/plans/fields.go
index f2a8b7edcb772..fc2cf64ec07eb 100644
--- a/plan/plans/fields.go
+++ b/plan/plans/fields.go
@@ -22,6 +22,7 @@ import (
 	"github.com/pingcap/tidb/context"
 	"github.com/pingcap/tidb/expression"
 	"github.com/pingcap/tidb/field"
+	"github.com/pingcap/tidb/mysql"
 	"github.com/pingcap/tidb/plan"
 	"github.com/pingcap/tidb/util/format"
 	"github.com/pingcap/tidb/util/types"
@@ -83,7 +84,7 @@ func (r *SelectFieldsDefaultPlan) Next(ctx context.Context) (row *plan.Row, err
 		}
 		di, ok := d.(*types.DataItem)
 		if ok {
-			if r.ResultFields[i].Col.Tp == 0 {
+			if r.ResultFields[i].Col.Tp == mysql.UnInitializedType {
 				r.ResultFields[i].Col.FieldType = *di.Type
 			}
 			row.Data[i] = di.Data
diff --git a/plan/plans/plans.go b/plan/plans/plans.go
index d682b06eb7d33..1d13c3f99f618 100644
--- a/plan/plans/plans.go
+++ b/plan/plans/plans.go
@@ -131,7 +131,7 @@ func setResultFieldInfo(fields []*field.ResultField, values []interface{}) error
 		return errors.Errorf("Fields and Values length unmatch %d VS %d", len(fields), len(values))
 	}
 	for i, rf := range fields {
-		if rf.Col.Tp == 0 {
+		if rf.Col.Tp == mysql.UnInitializedType {
 			// 0 == TypeDecimal, Tp maybe uninitialized
 			rf.Col.Charset = charset.CharsetBin
 			rf.Col.Collate = charset.CharsetBin
diff --git a/plan/plans/union.go b/plan/plans/union.go
index 5675a9666bae2..392205caf0a8c 100644
--- a/plan/plans/union.go
+++ b/plan/plans/union.go
@@ -19,7 +19,7 @@ import (
 	"github.com/pingcap/tidb/expression"
 	"github.com/pingcap/tidb/field"
 	"github.com/pingcap/tidb/kv/memkv"
-	mysql "github.com/pingcap/tidb/mysqldef"
+	"github.com/pingcap/tidb/mysql"
 	"github.com/pingcap/tidb/plan"
 	"github.com/pingcap/tidb/util/format"
 	"github.com/pingcap/tidb/util/types"