MySQL外键约束On Delete、On Update

使用外键实现
Create Table: CREATE TABLE `child` (
  `par_id` int(11) NOT NULL,
  `child_id` int(11) NOT NULL,
      PRIMARY KEY (`par_id`,`child_id`),
      FOREIGN KEY (`par_id`)   REFERENCES `parent` (`par_id`) 
        ON DELETE CASCADE 
        ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8



Create Table: CREATE TABLE `parent` (
  `par_id` int(11) NOT NULL,
  PRIMARY KEY (`par_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8

使用mysql trigger实现
mysql> show   triggers\G$
*************************** 1. row ***************************
             Trigger: t12
               Event: UPDATE
               Table: t3
           Statement: begin
        update  t4 set  tid = new.id   where  tid = old.id;
        end
              Timing: AFTER
             Created: NULL
            sql_mode: NO_ENGINE_SUBSTITUTION
             Definer: root@localhost
character_set_client: gbk
collation_connection: gbk_chinese_ci
  Database Collation: utf8_general_ci
*************************** 2. row ***************************
             Trigger: t11
               Event: DELETE
               Table: t3
           Statement: begin
        update  t4 set  tid = 0     where  tid = old.id;
        end
              Timing: AFTER
             Created: NULL
            sql_mode: NO_ENGINE_SUBSTITUTION
             Definer: root@localhost
character_set_client: gbk
collation_connection: gbk_chinese_ci
  Database Collation: utf8_general_ci
2 rows in set (0.02 sec)