猿哥解讀

本文的亮點在于很多PHPer肯定不知道MySQL還能這么用。

所周知，目前的mysql版本中并不支持直接的遞歸查詢，但是通過遞歸到迭代轉化的思路，還是可以在一句SQL內實現樹的遞歸查詢的。這個得益于Mysql允許在SQL語句內使用@變量。以下是示例代碼。

創建表格

CREATE TABLE `treenodes` (

`id` int , -- 節點ID

`nodename` varchar (60), -- 節點名稱

`pid` int -- 節點父ID

);

插入測試數據

INSERT INTO `treenodes` (`id`, `nodename`, `pid`) VALUES

('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'),('18','R','3'),

('19','S','2'),('20','T','6'),('21','U','8');

查詢語句

SELECT id AS ID,pid AS 父ID ,levels AS 父到子之間級數, paths AS 父到子路徑 FROM (

SELECT id,pid,

@le:= IF (pid = 0 ,0,

IF( LOCATE( CONCAT('|',pid,':'),@pathlevel) > 0 ,

SUBSTRING_INDEX( SUBSTRING_INDEX(@pathlevel,CONCAT('|',pid,':'),-1),'|',1) +1

,@le+1) ) levels

, @pathlevel:= CONCAT(@pathlevel,'|',id,':', @le ,'|') pathlevel

, @pathnodes:= IF( pid =0,',0',

CONCAT_WS(',',

IF( LOCATE( CONCAT('|',pid,':'),@pathall) > 0 ,

SUBSTRING_INDEX( SUBSTRING_INDEX(@pathall,CONCAT('|',pid,':'),-1),'|',1)

,@pathnodes ) ,pid ) )paths

,@pathall:=CONCAT(@pathall,'|',id,':', @pathnodes ,'|') pathall

FROM treenodes,

(SELECT @le:=0,@pathlevel:='', @pathall:='',@pathnodes:='') vv

ORDER BY pid,id

) src

ORDER BY id

最后的結果如下：

ID?? 父ID????父到子之間級數? 父到子路徑

------?? ?------??? ?--------------------????-------------------

1?????? 0?????????? ?? 0????????????????? ?? ,0

2?????? 1??????????? ? 1??????????????????? ?,0,1

3?????? 1???????????? ?1?????????????????? ? ,0,1

4?????? 2???????????? ?2???????????????????? ,0,1,2

5?????? 2????????????? 2??????????????????? ?,0,1,2

6?????? 3????????????? 2?????????????????? ? ,0,1,3

7?????? 6??????????? ? 3?????????????????? ? ,0,1,3,6

8?????? 0??????????? ? 0??????????????????? ?,0

9?????? 8????????????? 1?????????????????????,0,8

10?????? 8???????????? 1?????????????????????,0,8

11?????? 8??????????? ?1?????????????????? ? ,0,8

12?????? 9??????????? ?2?????????????????????,0,8,9

13?????? 9?????????? ? 2??????????????????? ?,0,8,9

14????? 12????????? ? 3???????????????????? ?,0,8,9,12

15????? 12?????????? ?3??????????????????? ?,0,8,9,12

16????? 15????????? ? 4??????????????????? ?,0,8,9,12,15

17????? 15??????????? 4??????????????????? ?,0,8,9,12,15

18?????? 3??????????? 2?????????????????? ?? ,0,1,3

19?????? 2??????????? 2??????????????????? ? ,0,1,2

20?????? 6?????????? ?3??????????????????? ? ,0,1,3,6

21?????? 8?????????? ?1??????????????????? ? ,0,8

以上就是一句SQL實現MYSQL的遞歸查詢的實現全過程，希望對大家的學習有所幫助。

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