Mysql 多表关联查询和删除

三表 关联 Left join  查询 ,更多表 以次类推：

组织表：

CREATE TABLE `t_organization` (
  `organization_id` int(11) NOT NULL,
  `name` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`organization_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of t_organization
-- ----------------------------
INSERT INTO `t_organization` VALUES ('101', '组织一');
INSERT INTO `t_organization` VALUES ('102', '组织二');
INSERT INTO `t_organization` VALUES ('103', '组织三');
INSERT INTO `t_organization` VALUES ('104', '组织四');

部门表：

CREATE TABLE `t_department` (
  `department_id` int(11) NOT NULL,
  `organization_id` int(11) DEFAULT NULL,
  `name` varchar(255) DEFAULT NULL,
  `position` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`department_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of t_department
-- ----------------------------
INSERT INTO `t_department` VALUES ('1001', '101', '部门一', '地址一');
INSERT INTO `t_department` VALUES ('1002', '101', '部门二', '地址二');
INSERT INTO `t_department` VALUES ('1003', null, '部门三', '地址三');
INSERT INTO `t_department` VALUES ('1004', '102', '部门四', '地址四');

用户表：

CREATE TABLE `t_user` (
  `user_id` int(11) NOT NULL,
  `department_id` int(11) DEFAULT NULL,
  `name` varchar(255) DEFAULT NULL,
  `age` int(11) DEFAULT NULL,
  `sex` varchar(255) DEFAULT NULL,
  `note` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`user_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of t_user
-- ----------------------------
INSERT INTO `t_user` VALUES ('1', '1001', 'Jesse', '20', '0', null);
INSERT INTO `t_user` VALUES ('2', '1001', 'Jack', '22', '1', null);
INSERT INTO `t_user` VALUES ('3', '1002', 'Tom', '19', '1', null);
INSERT INTO `t_user` VALUES ('4', null, 'Edward', '25', '0', 'note');

组织表：

部门表：

用户表：

 

两张表关联：

三张表关联：

在两张表的基础上，继续左链接

SELECT
	*
FROM
	t_organization AS o
LEFT JOIN t_department AS d ON o.organization_id = d.organization_id
LEFT JOIN t_user AS u ON d.department_id = u.department_id

 

拓展：

三表关联删除

delete t1,t2,t3 from doorlock as t1 left join alarm as t2  on t1.id= t2.device_id  left join simcard as  t3 on t1.id=t3.device_id

where t1.id= 28519;

alarm 告警表 ，simcard 表，doorlock 锁设备表

删除doorlock锁设备，simcard 和alarm 告警也须要相应删除 ,须要左链接 删除 ，由于 可能  锁设备存在，可是这个锁设备id 对应的告警表和simcard表 是不存在的

因此是 左链接 2次 删除

再拓展：

执行批量的删除

<delete id="batchDeleteDoorlock" parameterType="java.util.List">
    delete t1,t2,t3 from doorlock as t1 left join alarm as t2  on t1.id= t2.device_id  left join simcard as  t3 on t1.id=t3.device_id where id in

    <foreach collection="list" item="id" separator="," open="(" close=")">
      #{id}
    </foreach>
  </delete>