一句SQL实现MYSQL的递归查询

2015-07-31 10:48 dukou 阅读(44189) 评论(3) 编辑收藏举报

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
    ) src
ORDER 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

标签 Mysql , 递归 , 迭代 , 查询 , SQL