title: MySQL won't let me add a foreign key contstraint
body: <p>I am trying to add a foreign key like so, I am using MySQL Workbench, but I fail:</p>
  
  <pre><code>ALTER TABLE `db_name`.`tr_role_menu_item` ADD CONSTRAINT `fk_role`
  FOREIGN KEY (`fk_id_role`) REFERENCES `db_name`.`t_role` (`id_role`) ON
  DELETE NO ACTION ON
  UPDATE NO ACTION,
            ADD CONSTRAINT `fk_menu_item`
  FOREIGN KEY (`fk_id_menu_item`) REFERENCES `db_name`.`t_menu_item` (`id_menu_item`) ON
  DELETE NO ACTION ON
  UPDATE NO ACTION;
  </code></pre>
  
  <p>This is what Workbench outputs:</p>
  
  <pre><code>ERROR 1005: Can't create table 'db_name.#sql-659_c11' (errno: 150)
  ERROR: Error when running failback script. Details follow.
  ERROR 1050: Table 'tr_role_menu_item' already exists
  
  SQL Statement:
  
  CREATE TABLE `tr_role_menu_item` (
  
  `id_role_menu_item` int(11) NOT NULL AUTO_INCREMENT,
  
  `fk_id_role` int(11) NOT NULL,
  
  `fk_id_menu_item` int(11) NOT NULL,
  
   PRIMARY KEY (`id_role_menu_item`),
  
   KEY `fk_role_idx` (`fk_id_role`),
  
   KEY `fk_menu_item_idx` (`fk_id_menu_item`)
  
   ) ENGINE=InnoDB DEFAULT CHARSET=latin1
  </code></pre>
  
  <p>Any Help Please?</p>