SQL如何实现MYSQL的递归查询_Sql Server

SQL如何实现MYSQL的递归查询

2020-04-16 15:21dukou Sql Server

这篇文章主要介绍了根据递归到迭代转化的思路，利用SQL实现了MYSQL的递归查询,需要的朋友可以参考下

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

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									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

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									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

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									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