經常在一個表中有父子關系的兩個字段，比如empno與manager，這種結構中需要用到樹的遍歷。在Oracle 中可以使用connect by簡單解決問題，但MySQL 5.1中還不支持（據說已納入to do中），要自己寫過程或函數來實現。
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,'首頁',-1),
(14,'TV580',-1),
(15,'生活580',-1),
(16,'左上幻燈片',13),
(17,'幫忙',14),
(18,'欄目簡介',17);
DELIMITER $$
USE `db1`$$
-- 從某節點向下遍歷子節點
-- 遞歸生成臨時表數據
DROP PROCEDURE IF EXISTS `createChildLst`$$
CREATE PROCEDURE `createChildLst`(IN rootId INT,IN nDepth INT)
BEGIN
DECLARE done INT DEFAULT 0;
DECLARE b INT;
DECLARE cur1 CURSOR FOR SELECT id FROM channel WHERE parent_id=rootId;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;
SET max_sp_recursion_depth=12;
INSERT INTO tmpLst VALUES (NULL,rootId,nDepth);
OPEN cur1;
FETCH cur1 INTO b;
WHILE done=0 DO
CALL createChildLst(b,nDepth+1);
FETCH cur1 INTO b;
END WHILE;
CLOSE cur1;
END$$
-- 從某節點向上追溯根節點
-- 遞歸生成臨時表數據
DROP PROCEDURE IF EXISTS `createParentLst`$$
CREATE PROCEDURE `createParentLst`(IN rootId INT,IN nDepth INT)
BEGIN
DECLARE done INT DEFAULT 0;
DECLARE b INT;
DECLARE cur1 CURSOR FOR SELECT parent_id FROM channel WHERE id=rootId;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;
SET max_sp_recursion_depth=12;
INSERT INTO tmpLst VALUES (NULL,rootId,nDepth);
OPEN cur1;
FETCH cur1 INTO b;
WHILE done=0 DO
CALL createParentLst(b,nDepth+1);
FETCH cur1 INTO b;
END WHILE;
CLOSE cur1;
END$$
-- 實現類似Oracle SYS_CONNECT_BY_PATH的功能
-- 遞歸過程輸出某節點id路徑
DROP PROCEDURE IF EXISTS `createPathLst`$$
CREATE PROCEDURE `createPathLst`(IN nid INT,IN delimit VARCHAR(10),INOUT pathstr VARCHAR(1000))
BEGIN
DECLARE done INT DEFAULT 0;
DECLARE parentid INT DEFAULT 0;
DECLARE cur1 CURSOR FOR
SELECT t.parent_id,CONCAT(CAST(t.parent_id AS CHAR),delimit,pathstr)
FROM channel AS t WHERE t.id = nid;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;
SET max_sp_recursion_depth=12;
OPEN cur1;
FETCH cur1 INTO parentid,pathstr;
WHILE done=0 DO
CALL createPathLst(parentid,delimit,pathstr);
FETCH cur1 INTO parentid,pathstr;
END WHILE;
CLOSE cur1;
END$$
-- 遞歸過程輸出某節點name路徑
DROP PROCEDURE IF EXISTS `createPathnameLst`$$
CREATE PROCEDURE `createPathnameLst`(IN nid INT,IN delimit VARCHAR(10),INOUT pathstr VARCHAR(1000))
BEGIN
DECLARE done INT DEFAULT 0;
DECLARE parentid INT DEFAULT 0;
DECLARE cur1 CURSOR FOR
SELECT t.parent_id,CONCAT(t.cname,delimit,pathstr)
FROM channel AS t WHERE t.id = nid;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;
SET max_sp_recursion_depth=12;
OPEN cur1;
FETCH cur1 INTO parentid,pathstr;
WHILE done=0 DO
CALL createPathnameLst(parentid,delimit,pathstr);
FETCH cur1 INTO parentid,pathstr;
END WHILE;
CLOSE cur1;
END$$
-- 調用函數輸出id路徑
DROP FUNCTION IF EXISTS `fn_tree_path`$$
CREATE FUNCTION `fn_tree_path`(nid INT,delimit VARCHAR(10)) RETURNS VARCHAR(2000) CHARSET utf8
BEGIN
DECLARE pathid VARCHAR(1000);
SET @pathid=CAST(nid AS CHAR);
CALL createPathLst(nid,delimit,@pathid);
RETURN @pathid;
END$$
-- 調用函數輸出name路徑
DROP FUNCTION IF EXISTS `fn_tree_pathname`$$
CREATE FUNCTION `fn_tree_pathname`(nid INT,delimit VARCHAR(10)) RETURNS VARCHAR(2000) CHARSET utf8
BEGIN
DECLARE pathid VARCHAR(1000);
SET @pathid='';
CALL createPathnameLst(nid,delimit,@pathid);
RETURN @pathid;
END$$
-- 調用過程輸出子節點
DROP PROCEDURE IF EXISTS `showChildLst`$$
CREATE PROCEDURE `showChildLst`(IN rootId INT)
BEGIN
DROP TEMPORARY TABLE IF EXISTS tmpLst;
CREATE TEMPORARY TABLE IF NOT EXISTS tmpLst
(sno INT PRIMARY KEY AUTO_INCREMENT,id INT,depth INT);
CALL createChildLst(rootId,0);
SELECT channel.id,CONCAT(SPACE(tmpLst.depth*2),'--',channel.cname) NAME,channel.parent_id,tmpLst.depth,fn_tree_path(channel.id,'/') path,fn_tree_pathname(channel.id,'/') pathname
FROM tmpLst,channel WHERE tmpLst.id=channel.id ORDER BY tmpLst.sno;
END$$
-- 調用過程輸出父節點
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 ;
1. 因為mysql對動態游標的支持不夠，所以要想做成通用的過程或函數比較困難，可以利用兩個臨時表來轉換（同時去掉了遞歸調用）是個相對通用的實現。
2. 目前來看無論哪種實現，效率都不太好，希望mysql自己能實現Oracle 的connect by 功能，應該會比較優化。
