一句SQL实现MYSQL的递归查询

luoye 2021年06月14日数据库 305 0

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

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