樣例資料：
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)
樹形圖如下
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
建立乙個function getchildlst, 得到乙個由所有子節點號組成的字串.
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;
enddelimiter ;
使用我們直接利用find_in_set函式配合這個getchildlst來查詢
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 |
優點：簡單，方便，沒有遞迴呼叫層次深度的限制 (max_sp_recursion_depth,最大255);
缺點：長度受限，雖然可以擴大 returns varchar(1000)，但總是有最大限制的。
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