mysql循环查询树状数据

完整function

CREATE  FUNCTION `getChildList`(rootId BIGINT, table_name varchar(20)) RETURNS varchar(21845) CHARSET utf8
BEGIN
       DECLARE str VARCHAR(21845) ;
       DECLARE cid VARCHAR(21845) ; 

       SET str = '';
       SET cid =cast(rootId as CHAR); 

       WHILE cid is not null DO
         SET str= concat(str,',',cid);
                 IF table_name = 'tb_menu' THEN
                    SELECT group_concat(id) INTO cid from tb_menu where FIND_IN_SET(p_id,cid)>0;
                 ELSEIF table_name = 'tm_service_category' THEN
                    SELECT group_concat(pk_id) INTO cid FROM tm_service_category where FIND_IN_SET(p_id,cid)>0;
                 ELSEIF table_name = 'tm_part_category' THEN
                    SELECT group_concat(pk_id) INTO cid FROM tm_part_category  where is_del = 0 and FIND_IN_SET(p_id,cid)>0;
                 end IF;
       END WHILE;
       RETURN str;
END

mysql查询树解析（此处只是简单的循环并非递归）：
例如：调用如下

select getChildList(0,tm_service_category)

提炼执行语句

       WHILE cid is not null DO
         SET str= concat(str,',',cid);
            SELECT group_concat(pk_id) INTO cid FROM tm_service_category where FIND_IN_SET(p_id,cid)>0;
       END WHILE;
       RETURN str;
        END

tm_service_category 表结构如下

CREATE TABLE `tm_service_category` (
  `pk_id` bigint(20) unsigned NOT NULL COMMENT '主键',
  `name` varchar(50) DEFAULT NULL COMMENT '名称',
  `p_id` bigint(20) unsigned DEFAULT NULL COMMENT '父节点',
  PRIMARY KEY (`pk_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 ROW_FORMAT=COMPACT;

最主要的是p_id字段，表示父节点的pk_id

假设有数据如下

pk_id	p_id	name
1	0	a
2	1	b
3	1	c
4	2	d

树结构如下：

整棵树的根节点为0，二级节点1，三级节点为2，3，四级节点为4

模拟执行循环语句

       WHILE cid is not null DO
         SET str= concat(str,',',cid);
            SELECT group_concat(pk_id) INTO cid FROM tm_service_category where FIND_IN_SET(p_id,cid)>0;
       END WHILE;
       RETURN str;
        END

getChildList(0,tm_service_category)

1，初始化cid=0
2，查找p_id为0的所有节点拿到所有二级节点赋值给cid，cid=1，str=0,1
3，重复2步操作，查找p_id为1的所有节点拿到所有二级节点赋值给cid,cid=2,3,str=0,1,2,3
4，重复2步操作，查找p_id为2,3的所有节点拿到所有三级节点赋值给cid,cid=4,str=0,1,2,3,4
5，重复2步操作，查找p_id为4的所有节点赋值给cid，没找到任何节点,cid=null,退出循环