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[数据库]一句SQL实现MYSQL的递归查询


众所周知,目前的mysql版本中并不支持直接的递归查询,但是通过递归到迭代转化的思路,还是可以在一句SQL内实现树的递归查询的。这个得益于Mysql允许在SQL语句内使用@变量。以下是示例代码。

创建表格

CREATE TABLE `treenodes` (  `id` int , -- 节点ID  `nodename` varchar (60), -- 节点名称  `pid` int -- 节点父ID); 

插入测试数据

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');

查询语句

 SELECT id AS ID,pid AS 父ID ,levels AS 父到子之间级数, paths AS 父到子路径 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  ) srcORDER BY id

最后的结果如下:

  ID  父ID 父到子之间级数 父到子路径------ ------ ------------ ---------------   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