样例数据：
create table treeNodes(
id int primary key,
nodename varchar(20),
pid int
);
select * from treeNodes;
+----+----------+------+
| id | nodename | pid |
+----+----------+------+
| 1 | A | 0 |
| 2 | B | 1 |
| 3 | C | 1 |
| 4 | D | 2 |
| 5 | E | 2 |
| 6 | F | 3 |
| 7 | G | 6 |
| 8 | H | 0 |
| 9 | I | 8 |
| 10 | J | 8 |
| 11 | K | 8 |
| 12 | L | 9 |
| 13 | M | 9 |
| 14 | N | 12 |
| 15 | O | 12 |
| 16 | P | 15 |
| 17 | Q | 15 |
+----+----------+------+
17 rows in set (0.00 sec)树形图如下
1:A
+-- 2:B
| +-- 4:D
| +-- 5:E
+-- 3:C
+-- 6:F
+-- 7:G
8:H
+-- 9:I
| +-- 12:L
| | +--14:N
| | +--15:O
| | +--16:P
| | +--17:Q
| +-- 13:M
+-- 10:J
+-- 11:K 创建一个function getChildLst, 得到一个由所有子节点号组成的字符串.
delimiter //
CREATE FUNCTION `getChildLst`(rootId INT)
RETURNS varchar(1000)
BEGIN
DECLARE sTemp VARCHAR(1000);
DECLARE sTempChd VARCHAR(1000);
SET sTemp = ‘$‘;
SET sTempChd =cast(rootId as CHAR);
WHILE sTempChd is not null DO
SET sTemp = concat(sTemp,‘,‘,sTempChd);
SELECT group_concat(id) INTO sTempChd FROM treeNodes where FIND_IN_SET(pid,sTempChd)>0;
END WHILE;
RETURN sTemp;
END
//
delimiter ;使用我们直接利用find_in_set函数配合这个getChildlst来查找
select getChildLst(1);
+-----------------+
| getChildLst(1) |
+-----------------+
| $,1,2,3,4,5,6,7 |
+-----------------+
select * from treeNodes where FIND_IN_SET(id, getChildLst(1));
+----+----------+------+
| id | nodename | pid |
+----+----------+------+
| 1 | A | 0 |
| 2 | B | 1 |
| 3 | C | 1 |
| 4 | D | 2 |
| 5 | E | 2 |
| 6 | F | 3 |
| 7 | G | 6 |
+----+----------+------+
select * from treeNodes where FIND_IN_SET(id, getChildLst(3));
+----+----------+------+
| id | nodename | pid |
+----+----------+------+
| 3 | C | 1 |
| 6 | F | 3 |
| 7 | G | 6 |
+----+----------+------+优点：简单，方便，没有递归调用层次深度的限制 (max_sp_recursion_depth,最大255);
缺点：长度受限，虽然可以扩大 RETURNS varchar(1000)，但总是有最大限制的。
