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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