SQL如何實現MYSQL的遞歸查詢

2020-07-25 12:52:36

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來源：轉載

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眾所周知，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  ) srcORDER 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