MySQL 實現樹的遍歷詳解及簡單實現示例，mysql示例

MySQL 實現樹的遍歷詳解及簡單實現示例，mysql示例

MySQL 實現樹的遍歷

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。

一、建立測試表和數據：

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); 

 二、利用臨時表和遞歸過程實現樹的遍歷（MySQL的UDF不能遞歸調用）：

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 ; 

三、測試

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、遺留問題

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。

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