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。

感谢阅读，希望能帮助到大家，谢谢大家对本站的支持！