MySQL 实现树的遍历详解及简单实现示例

数据库  /  管理员 发布于 6年前   157

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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