Fixed Empty Returning Clause Merge Bug (#7339)

clause/returning.go

@@ -26,9 +26,12 @@ func (returning Returning) Build(builder Builder) {
 
 // MergeClause merge order by clauses
 func (returning Returning) MergeClause(clause *Clause) {
-	if v, ok := clause.Expression.(Returning); ok {
+	if v, ok := clause.Expression.(Returning); ok && len(returning.Columns) > 0 {
-		returning.Columns = append(v.Columns, returning.Columns...)
+		if v.Columns != nil {
+			returning.Columns = append(v.Columns, returning.Columns...)
+		} else {
+			returning.Columns = nil
+		}
 	}
-
 	clause.Expression = returning
 }

clause/returning_test.go

@@ -26,6 +26,22 @@ func TestReturning(t *testing.T) {
 			}},
 			"SELECT * FROM `users` RETURNING `users`.`id`,`name`,`age`", nil,
 		},
+		{
+			[]clause.Interface{clause.Select{}, clause.From{}, clause.Returning{
+				[]clause.Column{clause.PrimaryColumn},
+			}, clause.Returning{}, clause.Returning{
+				[]clause.Column{{Name: "name"}, {Name: "age"}},
+			}},
+			"SELECT * FROM `users` RETURNING *", nil,
+		},
+		{
+			[]clause.Interface{clause.Select{}, clause.From{}, clause.Returning{
+				[]clause.Column{clause.PrimaryColumn},
+			}, clause.Returning{
+				[]clause.Column{{Name: "name"}, {Name: "age"}},
+			}, clause.Returning{}},
+			"SELECT * FROM `users` RETURNING *", nil,
+		},
 	}
 
 	for idx, result := range results {