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

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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