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《MYSQL教程mysql递归查询实现方法》要点：
本文介绍了MYSQL教程mysql递归查询实现方法，希望对您有用。如果有疑问，可以联系我们。
导读：在Oracle 中有一个 Hierarchical Queries 通过CONNECT BY 可以方便的查了所有当前节点下的所有子节点.在MySQL的目前版本中还没有对...
MYSQL应用在Oracle 中有一个 Hierarchical Queries 通过CONNECT BY 可以方便的查了所有当前节点下的所有子节点.
在MySQL的目前版本中还没有对应的功能.
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在MySQL中如果是有限的层次,比如事先如果可以确定这个树的最大深度是4,那么所有节点为根的树的深度均不会超过4,则可以直接通过left join 来实现.
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但有时无法控制树的深度.这时就需要在MySQL中用存储过程来实现或在你的程序中来实现这个递归.
MYSQL应用本文讨论一下几种实现的办法.
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样例数据：
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mysql> create table treeNodes
??? -> (
??? ->? id int primary key,
??? ->? nodename varchar(20),
??? ->? pid int
??? -> );
Query OK,0 rows affected (0.09 sec)
mysql> select * from treenodes;
+----+----------+------+
| id | nodename | pid? |
+----+----------+------+
|? 1 | A??????? |??? 0 |
|? 2 | B??????? |??? 1 |
|? 3 | C??????? |??? 1 |
|? 4 | D??????? |??? 2 |
|? 5 | E??????? |??? 2 |
|? 6 | F??????? |??? 3 |
|? 7 | G??????? |??? 6 |
|? 8 | H??????? |??? 0 |
|? 9 | I??????? |??? 8 |
| 10 | J??????? |??? 8 |
| 11 | K??????? |??? 8 |
| 12 | L??????? |??? 9 |
| 13 | M??????? |??? 9 |
| 14 | N??????? |?? 12 |
| 15 | O??????? |?? 12 |
| 16 | P??????? |?? 15 |
| 17 | Q??????? |?? 15 |
+----+----------+------+
17 rows in set (0.00 sec)
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MYSQL应用树形图：
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1:A
? +-- 2:B
? |??? +-- 4:D
? |??? +-- 5:E
? +-- 3:C
?????? +-- 6:F
??????????? +-- 7:G
?8:H
? +-- 9:I
? |??? +-- 12:L
? |??? |??? +--14:N
? |??? |??? +--15:O
? |??? |??????? +--16:P
? |??? |??????? +--17:Q
? |??? +-- 13:M
? +-- 10:J
? +-- 11:K?
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MYSQL应用?
办法一：利用函数来得到所有子节点号.
创建一个function getChildLst,得到一个由所有子节点号组成的字符串.
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MYSQL应用mysql> delimiter //
mysql>
mysql> CREATE FUNCTION `getChildLst`(rootId INT)
??? -> RETURNS varchar(1000)
??? -> BEGIN
??? ->?? DECLARE sTemp VARCHAR(1000);
??? ->?? DECLARE sTempChd VARCHAR(1000);
??? ->
??? ->?? SET sTemp = '$';
??? ->?? SET sTempChd =cast(rootId as CHAR);
??? ->
??? ->?? WHILE sTempChd is not null DO
??? ->???? SET sTemp = concat(sTemp,',sTempChd);
??? ->???? SELECT group_concat(id) INTO sTempChd FROM treeNodes where FIND_IN_SET(pid,sTempChd)>0;
??? ->?? END WHILE;
??? ->?? RETURN sTemp;
??? -> END
??? -> //
Query OK,0 rows affected (0.00 sec)
MYSQL应用mysql>
mysql> delimiter ;
MYSQL应用使用直接利用find_in_set函数配合这个getChildlst来查找：
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MYSQL应用mysql> select getChildLst(1);
+-----------------+
| getChildLst(1)? |
+-----------------+
| $,1,2,3,4,5,6,7 |
+-----------------+
1 row in set (0.00 sec)
MYSQL应用mysql> select * from treeNodes
??? -> where FIND_IN_SET(id,getChildLst(1));
+----+----------+------+
| id | nodename | pid? |
+----+----------+------+
|? 1 | A??????? |??? 0 |
|? 2 | B??????? |??? 1 |
|? 3 | C??????? |??? 1 |
|? 4 | D??????? |??? 2 |
|? 5 | E??????? |??? 2 |
|? 6 | F??????? |??? 3 |
|? 7 | G??????? |??? 6 |
+----+----------+------+
7 rows in set (0.01 sec)
MYSQL应用mysql> select * from treeNodes
??? -> where FIND_IN_SET(id,getChildLst(3));
+----+----------+------+
| id | nodename | pid? |
+----+----------+------+
|? 3 | C??????? |??? 1 |
|? 6 | F??????? |??? 3 |
|? 7 | G??????? |??? 6 |
+----+----------+------+
3 rows in set (0.01 sec)
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MYSQL应用优点: 简单,方便,没有递归调用层次深度的限制 (max_sp_recursion_depth,最大255) ；
缺点：长度受限,虽然可以扩大 RETURNS varchar(1000),但总是有最大限制的.
MySQL目前版本( 5.1.33-community)中还不支持function 的递归调用.
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办法二：利用临时表和过程递归
创建存储过程如下.createChildLst 为递归过程,showChildLst为调用入口过程,准备临时表及初始化.
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MYSQL应用mysql> delimiter //
mysql>
mysql> # 入口过程
mysql> CREATE PROCEDURE showChildLst (IN rootId INT)
??? -> BEGIN
??? ->? CREATE TEMPORARY TABLE IF NOT EXISTS tmpLst
??? ->?? (sno int primary key auto_increment,id int,depth int);
??? ->? DELETE FROM tmpLst;
??? ->
??? ->? CALL createChildLst(rootId,0);
??? ->
??? ->? select tmpLst.*,treeNodes.* from tmpLst,treeNodes where tmpLst.id=treeNodes.id order by tmpLst.sno;
??? -> END;
??? -> //
Query OK,0 rows affected (0.00 sec)
MYSQL应用mysql>
mysql> # 递归过程
mysql> 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 treeNodes where pid=rootId;
??? ->? DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;
??? ->
??? ->? 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;
??? -> //
Query OK,0 rows affected (0.00 sec)
mysql> delimiter ;
MYSQL应用调用时传入结点：
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MYSQL应用mysql> call showChildLst(1);
+-----+------+-------+----+----------+------+
| sno | id?? | depth | id | nodename | pid? |
+-----+------+-------+----+----------+------+
|?? 4 |??? 1 |???? 0 |? 1 | A??????? |??? 0 |
|?? 5 |??? 2 |???? 1 |? 2 | B??????? |??? 1 |
|?? 6 |??? 4 |???? 2 |? 4 | D??????? |??? 2 |
|?? 7 |??? 5 |???? 2 |? 5 | E??????? |??? 2 |
|?? 8 |??? 3 |???? 1 |? 3 | C??????? |??? 1 |
|?? 9 |??? 6 |???? 2 |? 6 | F??????? |??? 3 |
|? 10 |??? 7 |???? 3 |? 7 | G??????? |??? 6 |
+-----+------+-------+----+----------+------+
7 rows in set (0.13 sec)
MYSQL应用Query OK,0 rows affected,1 warning (0.14 sec)
MYSQL应用mysql>
mysql> call showChildLst(3);
+-----+------+-------+----+----------+------+
| sno | id?? | depth | id | nodename | pid? |
+-----+------+-------+----+----------+------+
|?? 1 |??? 3 |???? 0 |? 3 | C??????? |??? 1 |
|?? 2 |??? 6 |???? 1 |? 6 | F??????? |??? 3 |
|?? 3 |??? 7 |???? 2 |? 7 | G??????? |??? 6 |
+-----+------+-------+----+----------+------+
3 rows in set (0.11 sec)
MYSQL应用Query OK,1 warning (0.11 sec)
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MYSQL应用depth 为深度,这样可以在程序进行一些显示上的格式化处理.类似于oracle中的 level 伪列.sno 仅供排序控制.
这样还可以通过临时表tmpLst与数据库中其它表进行联接查询.
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MySQL中可以利用系统参数 max_sp_recursion_depth 来控制递归调用的层数上限.如下例设为12.
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mysql> set max_sp_recursion_depth=12;
Query OK,0 rows affected (0.00 sec)
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MYSQL应用?
优点 : 可以更灵活处理,及层数的显示.并且可以依照树的遍历顺序得到结果.
缺点 : 递归有255的限制.
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方法三：利用中间表和过程
(本方法由yongyupost2000提供样子改编)
创建存储过程如下.
由于MySQL中不允许在同一语句中对临时表多次引用,只以使用普通表tmpLst来实现了.
当然程序中负责在用完后清除这个表.
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delimiter //
drop PROCEDURE IF EXISTS? showTreeNodes_yongyupost2000//
CREATE PROCEDURE showTreeNodes_yongyupost2000 (IN rootid INT)
BEGIN
?DECLARE Level int ;
?drop TABLE IF EXISTS tmpLst;
?CREATE TABLE tmpLst (
? id int,
? nLevel int,
? sCort varchar(8000)
?);
?
?Set Level=0 ;
?INSERT into tmpLst SELECT id,Level,ID FROM treeNodes WHERE PID=rootid;
?WHILE ROW_COUNT()>0 DO
? SET Level=Level+1 ;
? INSERT into tmpLst
?? SELECT A.ID,concat(B.sCort,A.ID) FROM treeNodes A,tmpLst B
??? WHERE? A.PID=B.ID AND B.nLevel=Level-1? ;
?END WHILE;
?
END;
//
delimiter ;
CALL showTreeNodes_yongyupost2000(0);
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MYSQL应用执行完后会产生一个tmpLst表,nLevel 为节点深度,sCort 为排序字段.
使用办法：
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SELECT concat(SPACE(B.nLevel*2),'+--',A.nodename)
FROM treeNodes A,tmpLst B
WHERE A.ID=B.ID
ORDER BY B.sCort;
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+--------------------------------------------+
| concat(SPACE(B.nLevel*2),A.nodename) |
+--------------------------------------------+
| +--A?????????????????????????????????????? |
|?? +--B???????????????????????????????????? |
|???? +--D?????????????????????????????????? |
|???? +--E?????????????????????????????????? |
|?? +--C???????????????????????????????????? |
|???? +--F?????????????????????????????????? |
|?????? +--G???????????????????????????????? |
| +--H?????????????????????????????????????? |
|?? +--J???????????????????????????????????? |
|?? +--K???????????????????????????????????? |
|?? +--I???????????????????????????????????? |
|???? +--L?????????????????????????????????? |
|?????? +--N???????????????????????????????? |
|?????? +--O???????????????????????????????? |
|???????? +--P?????????????????????????????? |
|???????? +--Q?????????????????????????????? |
|???? +--M?????????????????????????????????? |
+--------------------------------------------+
17 rows in set (0.00 sec)
MYSQL应用以上介绍了mysql递归查询的实现办法与实例代码,希望对大家有所帮助. 《MYSQL教程mysql递归查询实现方法》是否对您有启发，欢迎查看更多与《MYSQL教程mysql递归查询实现方法》相关教程，学精学透。编程之家PHP学院为您提供精彩教程。 （编辑：李大同）
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