mysql 使用成员变量，查询tree型结构数据

SELECT item.id,@a := item.parent_id parentId,item.item_name from item,(select @a:=(SELECT 1 from dual),@p:=0) vg
where item.id = @a

DROP TABLE IF EXISTS `item`;
CREATE TABLE `item` (
  `id` varchar(11) CHARACTER SET utf8 NOT NULL,
  `parent_id` varchar(11) CHARACTER SET utf8 DEFAULT NULL,
  `item_name` varchar(11) CHARACTER SET utf8 DEFAULT NULL,
  `path_id` varchar(22) CHARACTER SET utf8 DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

-- ----------------------------
-- Records of item
-- ----------------------------
INSERT INTO `item` VALUES ('1', '2', '财政部', '1');
INSERT INTO `item` VALUES ('2', '3', '人事部', '2');
INSERT INTO `item` VALUES ('3', '4', '销售部', '3');
INSERT INTO `item` VALUES ('4', '', '总部', '4');
INSERT INTO `item` VALUES ('5', '4', '吹牛部门', '5');
INSERT INTO `item` VALUES ('6', '4', '后勤部', '6');