anyCrease should have value

class/campaigns.php

@@ -12,13 +12,13 @@ class Campaigns
         $this->database = $database;
     }
 
-    public function decreaseAmountById( $id )
+    public function decreaseAmountById( $id, $value = 1 )
     {
-        $sql = 'UPDATE `'. DB_PREFIX . '_gebuchte_werbung` SET `menge` = `menge` -1 WHERE `id`= :id';
+        $sql = 'UPDATE `'. DB_PREFIX . '_gebuchte_werbung` SET `menge` = `menge` - :value WHERE `id`= :id';
         $sql_params = array(
                            ':id' => $id,
+                           ':value' => $value
                       );
-
         return $this->database->sqlUpdate($sql, $sql_params);
     }