MySQL 实现树的遍历详解及简单实现示例

MySQL 实现树的遍历

经常在一个表中有父子关系的两个字段，比如empno与manager，这种结构中需要用到树的遍历。在Oracle 中可以使用connect by简单解决问题，但MySQL 5.1中还不支持（据说已纳入to do中），要自己写过程或函数来实现。

一、建立测试表和数据：

DROP TABLE IF EXISTS `channel`; 

CREATE TABLE `channel` ( 
 `id` int(11) NOT NULL AUTO_INCREMENT,  
 `cname` varchar(200) DEFAULT NULL, 
 `parent_id` int(11) DEFAULT NULL, 
 PRIMARY KEY (`id`) 
) ENGINE=MyISAM AUTO_INCREMENT=19 DEFAULT CHARSET=utf8; 

/*Data for the table `channel` */ 

insert into `channel`(`id`,`cname`,`parent_id`)  
values (13,'首页',-1), 
    (14,'TV580',-1), 
    (15,'生活580',-1), 
    (16,'左上幻灯片',13), 
    (17,'帮忙',14), 
    (18,'栏目简介',17); 

二、利用临时表和递归过程实现树的遍历（MySQL的UDF不能递归调用）：

DELIMITER $$ 

USE `db1`$$ 

-- 从某节点向下遍历子节点 
-- 递归生成临时表数据 
DROP PROCEDURE IF EXISTS `createChildLst`$$ 

CREATE PROCEDURE `createChildLst`(IN rootId INT,IN nDepth INT) 
BEGIN 
   DECLARE done INT DEFAULT 0; 
   DECLARE b INT; 
   DECLARE cur1 CURSOR FOR SELECT id FROM channel WHERE parent_id=rootId; 
   DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1; 
   SET max_sp_recursion_depth=12; 

   INSERT INTO tmpLst VALUES (NULL,rootId,nDepth); 

   OPEN cur1; 

   FETCH cur1 INTO b; 
   WHILE done=0 DO 
       CALL createChildLst(b,nDepth+1); 
       FETCH cur1 INTO b; 
   END WHILE; 

   CLOSE cur1; 
   END$$ 

-- 从某节点向上追溯根节点 
-- 递归生成临时表数据 
DROP PROCEDURE IF EXISTS `createParentLst`$$ 

CREATE PROCEDURE `createParentLst`(IN rootId INT,IN nDepth INT) 
BEGIN 
   DECLARE done INT DEFAULT 0; 
   DECLARE b INT; 
   DECLARE cur1 CURSOR FOR SELECT parent_id FROM channel WHERE id=rootId; 
   DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1; 
   SET max_sp_recursion_depth=12; 

   INSERT INTO tmpLst VALUES (NULL,rootId,nDepth); 

   OPEN cur1; 

   FETCH cur1 INTO b; 
   WHILE done=0 DO 
       CALL createParentLst(b,nDepth+1); 
       FETCH cur1 INTO b; 
   END WHILE; 

   CLOSE cur1; 
   END$$ 

-- 实现类似Oracle SYS_CONNECT_BY_PATH的功能 
-- 递归过程输出某节点id路径 
DROP PROCEDURE IF EXISTS `createPathLst`$$ 

CREATE PROCEDURE `createPathLst`(IN nid INT,IN delimit VARCHAR(10),INOUT pathstr VARCHAR(1000)) 
BEGIN          
   DECLARE done INT DEFAULT 0; 
   DECLARE parentid INT DEFAULT 0;    
   DECLARE cur1 CURSOR FOR  
   SELECT t.parent_id,CONCAT(CAST(t.parent_id AS CHAR),delimit,pathstr) 
    FROM channel AS t WHERE t.id = nid; 

   DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1; 
   SET max_sp_recursion_depth=12;          

   OPEN cur1; 

   FETCH cur1 INTO parentid,pathstr; 
   WHILE done=0 DO       
       CALL createPathLst(parentid,delimit,pathstr); 
       FETCH cur1 INTO parentid,pathstr; 
   END WHILE; 

   CLOSE cur1;  
   END$$ 

-- 递归过程输出某节点name路径 
DROP PROCEDURE IF EXISTS `createPathnameLst`$$ 

CREATE PROCEDURE `createPathnameLst`(IN nid INT,IN delimit VARCHAR(10),INOUT pathstr VARCHAR(1000)) 
BEGIN          
   DECLARE done INT DEFAULT 0; 
   DECLARE parentid INT DEFAULT 0;    
   DECLARE cur1 CURSOR FOR  
   SELECT t.parent_id,CONCAT(t.cname,delimit,pathstr) 
    FROM channel AS t WHERE t.id = nid; 

   DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1; 
   SET max_sp_recursion_depth=12;          

   OPEN cur1; 

   FETCH cur1 INTO parentid,pathstr; 
   WHILE done=0 DO       
       CALL createPathnameLst(parentid,delimit,pathstr); 
       FETCH cur1 INTO parentid,pathstr; 
   END WHILE; 

   CLOSE cur1;  
   END$$ 

-- 调用函数输出id路径 
DROP FUNCTION IF EXISTS `fn_tree_path`$$ 

CREATE FUNCTION `fn_tree_path`(nid INT,delimit VARCHAR(10)) RETURNS VARCHAR(2000) CHARSET utf8 
BEGIN  
 DECLARE pathid VARCHAR(1000); 

 SET @pathid=CAST(nid AS CHAR); 
 CALL createPathLst(nid,delimit,@pathid); 

 RETURN @pathid; 
END$$ 

-- 调用函数输出name路径 
DROP FUNCTION IF EXISTS `fn_tree_pathname`$$ 

CREATE FUNCTION `fn_tree_pathname`(nid INT,delimit VARCHAR(10)) RETURNS VARCHAR(2000) CHARSET utf8 
BEGIN  
 DECLARE pathid VARCHAR(1000); 

 SET @pathid='';   
 CALL createPathnameLst(nid,delimit,@pathid); 

 RETURN @pathid; 
END$$ 

-- 调用过程输出子节点 
DROP PROCEDURE IF EXISTS `showChildLst`$$ 

CREATE PROCEDURE `showChildLst`(IN rootId INT) 
BEGIN 
   DROP TEMPORARY TABLE IF EXISTS tmpLst; 
   CREATE TEMPORARY TABLE IF NOT EXISTS tmpLst  
    (sno INT PRIMARY KEY AUTO_INCREMENT,id INT,depth INT);    

   CALL createChildLst(rootId,0); 

   SELECT channel.id,CONCAT(SPACE(tmpLst.depth*2),'--',channel.cname) NAME,channel.parent_id,tmpLst.depth,fn_tree_path(channel.id,'/') path,fn_tree_pathname(channel.id,'/') pathname 
   FROM tmpLst,channel WHERE tmpLst.id=channel.id ORDER BY tmpLst.sno; 
   END$$ 

-- 调用过程输出父节点 
DROP PROCEDURE IF EXISTS `showParentLst`$$ 

CREATE PROCEDURE `showParentLst`(IN rootId INT) 
BEGIN 
   DROP TEMPORARY TABLE IF EXISTS tmpLst; 
   CREATE TEMPORARY TABLE IF NOT EXISTS tmpLst  
    (sno INT PRIMARY KEY AUTO_INCREMENT,id INT,depth INT);    

   CALL createParentLst(rootId,0); 

   SELECT channel.id,CONCAT(SPACE(tmpLst.depth*2),'--',channel.cname) NAME,channel.parent_id,tmpLst.depth,fn_tree_path(channel.id,'/') path,fn_tree_pathname(channel.id,'/') pathname 
   FROM tmpLst,channel WHERE tmpLst.id=channel.id ORDER BY tmpLst.sno; 
   END$$ 

DELIMITER ; 

三、测试

CALL showChildLst(-1); 
CALL showChildLst(13); 
CALL showChildLst(14); 
CALL showChildLst(17); 
CALL showChildLst(18); 

CALL showParentLst(-1); 
CALL showParentLst(13); 
CALL showParentLst(14); 
CALL showParentLst(17); 
CALL showParentLst(18); 

四、遗留问题

1. 因为mysql对动态游标的支持不够，所以要想做成通用的过程或函数比较困难，可以利用两个临时表来转换（同时去掉了递归调用）是个相对通用的实现。

2. 目前来看无论哪种实现，效率都不太好，希望mysql自己能实现Oracle 的connect by 功能，应该会比较优化。

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