diff --git a/stmt/stmts/insert.go b/stmt/stmts/insert.go
index dcf3e830c6..ff83f31ec3 100644
--- a/stmt/stmts/insert.go
+++ b/stmt/stmts/insert.go
@@ -199,17 +199,17 @@ func (s *InsertIntoStmt) Exec(ctx context.Context) (_ rset.Recordset, err error)
 	}
 
 	for i, row := range rows {
-		// Notes: incompatible with mysql
-		// MySQL will set last insert id to the first row, as follows:
-		// `t(id int AUTO_INCREMENT, c1 int, PRIMARY KEY (id))`
-		// `insert t (c1) values(1),(2),(3);`
-		// Last insert id will be 1, not 3.
 		if len(s.OnDuplicate) == 0 {
 			txn.SetOption(kv.PresumeKeyNotExists, nil)
 		}
 		h, err := t.AddRecord(ctx, row, recordIDs[i])
 		txn.DelOption(kv.PresumeKeyNotExists)
 		if err == nil {
+			// Notes: incompatible with mysql
+			// MySQL will set last insert id to the first row, as follows:
+			// `t(id int AUTO_INCREMENT, c1 int, PRIMARY KEY (id))`
+			// `insert t (c1) values(1),(2),(3);`
+			// Last insert id will be 1, not 3.
 			variable.GetSessionVars(ctx).SetLastInsertID(uint64(recordIDs[i]))
 			continue
 		}
diff --git a/table/table.go b/table/table.go
index 932f6bd193..a5044c9e96 100644
--- a/table/table.go
+++ b/table/table.go
@@ -77,7 +77,7 @@ type Table interface {
 	// Truncate truncates the table.
 	Truncate(ctx context.Context) (err error)
 
-	// AddRecord inserts a row into the table.
+	// AddRecord inserts a row into the table. Is h is 0, it will alloc an unique id inside.
 	AddRecord(ctx context.Context, r []interface{}, h int64) (recordID int64, err error)
 
 	// UpdateRecord updates a row in the table.