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数据库对层次结构的处理模型有好多种，可以根据自己的需求来设计模型，当然最简单的也是最容易设计的模型就是所谓的邻接模型。在这方面，其他数据库比如Oracle 提供了现成的分析方法 connect by，而MySQL在这方面就显得有些薄弱了。 不过可以用MySQL的存储过程实现ORACLE类似的分析功能
这样，先来创建一个简单的数表。
create table country ( id number(2) not null, name varchar(60) not null); create table country_relation (id number(2), parentid number(2));
插入一些数据
-- Table country. insert into country (id,name) values (0,'Earth'); insert into country (id,name) values (2,'North America'); insert into country (id,name) values (3,'South America'); insert into country (id,name) values (4,'Europe'); insert into country (id,name) values (5,'Asia'); insert into country (id,name) values (6,'Africa'); insert into country (id,name) values (7,'Australia'); insert into country (id,name) values (8,'Canada'); insert into country (id,name) values (9,'Central America'); insert into country (id,name) values (10,'Island Nations'); insert into country (id,name) values (11,'United States'); insert into country (id,name) values (12,'Alabama'); insert into country (id,name) values (13,'Alaska'); insert into country (id,name) values (14,'Arizona'); insert into country (id,name) values (15,'Arkansas'); insert into country (id,name) values (16,'California');
-- Table country_relation. insert into country_relation (id,parentid) values (0,NULL); insert into country_relation (id,parentid) values (2,0); insert into country_relation (id,parentid) values (3,0); insert into country_relation (id,parentid) values (4,0); insert into country_relation (id,parentid) values (5,0); insert into country_relation (id,parentid) values (6,0); insert into country_relation (id,parentid) values (7,0); insert into country_relation (id,parentid) values (8,2); insert into country_relation (id,parentid) values (9,2); insert into country_relation (id,parentid) values (10,2); insert into country_relation (id,parentid) values (11,2); insert into country_relation (id,parentid) values (12,11); insert into country_relation (id,parentid) values (13,11); insert into country_relation (id,parentid) values (14,11); insert into country_relation (id,parentid) values (15,11); insert into country_relation (id,parentid) values (16,11);
在Oracle 里面，对这些操作就比较简单了，都是系统提供的。
比如下面四种情形：
1）. 查看深度，
select max(level) "level" from COUNTRY_RELATION a start with a.parentid is NULL connect by PRIOR a.id = a.PARENTID order by level; level ---------- 4 已用时间: 00: 00: 00.03
2）. 查看叶子节点
select name from ( select b.name, connect_by_isleaf "isleaf" from COUNTRY_RELATION a inner join country b on (a.id = b.id) start with a.parentid is NULL connect by prior a.id = a.PARENTID ) T where T."isleaf" = 1; NAME -------------------------------------------------- Canada Central America Island Nations Alabama Alaska Arizona Arkansas California South America Europe Asia Africa Australia 已选择13行。 已用时间: 00: 00: 00.01
3） 查看ROOT节点
select connect_by_root b.name from COUNTRY_RELATION a inner join country b on (a.id = b.id) start with a.parentid is NULL connect by a.id = a.PARENTID CONNECT_BY_ROOTB.NAME -------------------------------------------------- Earth 已用时间: 00: 00: 00.01
4）. 查看路径
select sys_connect_by_path(b.name,'/') "path" from COUNTRY_RELATION a inner join country b on (a.id = b.id) start with a.parentid is NULL connect by prior a.id = a.PARENTID order by level,a.id; path -------------------------------------------------- /Earth /Earth/North America /Earth/South America /Earth/Europe /Earth/Asia /Earth/Africa /Earth/Australia /Earth/North America/Canada /Earth/North America/Central America /Earth/North America/Island Nations /Earth/North America/United States /Earth/North America/United States/Alabama /Earth/North America/United States/Alaska /Earth/North America/United States/Arizona /Earth/North America/United States/Arkansas /Earth/North America/United States/California 已选择16行。 已用时间: 00: 00: 00.01
接下来我们看看在MySQL 里面如何实现上面四种情形：
前三种都比较简单，可以很容易写出SQL。
1）查看深度
mysql> SELECT COUNT(DISTINCT IFNULL(parentid,-1)) AS LEVEL FROM country_relation ; +-------+ | LEVEL | +-------+ | 4 | +-------+ 1 row in set (0.00 sec
)
2）查看ROOT节点
mysql> SELECT b.`name` AS root_node FROM -> ( -> SELECT id FROM country_relation WHERE parentid IS NULL -> ) AS a, country AS b WHERE a.id = b.id; +-----------+ | root_node | +-----------+ | Earth | +-----------+ 1 row in set (0.00 sec)
3). 查看叶子节点
mysql> SELECT b.`name` AS leaf_node FROM -> ( -> SELECT id FROM country_relation WHERE id NOT IN (SELECT IFNULL(parentid, -1) FROM country_relation) -> ) AS a, country AS b WHERE a.id = b.id; +-----------------+ | leaf_node | +-----------------+ | South America | | Europe | | Asia | | Africa | | Australia | | Canada | | Central America | | Island Nations | | Alabama | | Alaska | | Arizona | | Arkansas | | California | +-----------------+ 13 rows in set (0.00 sec) mysql>
4） 查看路径
这一块没有简单的SQL实现，不过可以用MySQL的存储过程来实现同样的功能。
存储过程代码如下：
DELIMITER $$
USE `t_girl`$$
DROP PROCEDURE IF EXISTS `sp_show_list`$$
CREATE DEFINER=`root`@`localhost` PROCEDURE `sp_show_list`()
BEGIN
-- Created by ytt 2014/11/04.
-- Is equal to oracle's connect by syntax.
-- Body.
DROP TABLE IF EXISTS tmp_country_list;
CREATE TEMPORARY TABLE tmp_country_list (node_level INT UNSIGNED NOT NULL, node_path VARCHAR(1000) NOT NULL);
-- Get the root node.
INSERT INTO tmp_country_list SELECT 1, CONCAT('/',id) FROM country_relation WHERE parentid IS NULL;
-- Loop within all parent node.
cursor1:BEGIN
DECLARE done1 INT DEFAULT 0;
DECLARE i1 INT DEFAULT 1;
DECLARE v_parentid INT DEFAULT -1;
DECLARE v_node_path VARCHAR(1000) DEFAULT '';
DECLARE cr1 CURSOR FOR SELECT parentid FROM country_relation WHERE parentid IS NOT NULL GROUP BY parentid ORDER BY parentid ASC;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done1 = 1;
OPEN cr1;
loop1:LOOP
FETCH cr1 INTO v_parentid;
IF done1 = 1 THEN
LEAVE loop1;
END IF;
SET i1 = i1 + 1;
label_path:BEGIN
DECLARE done2 INT DEFAULT 0;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done2 = 1;
-- Get the upper path.
SELECT node_path FROM tmp_country_list WHERE node_level = i1 - 1 AND LOCATE(v_parentid,node_path) > 0 INTO v_node_path;
-- Escape the outer not found exception.
IF done2 = 1 THEN
SET done2 = 0;
END IF;
INSERT INTO tmp_country_list
SELECT i1,CONCAT(IFNULL(v_node_path,''),'/',id) FROM country_relation WHERE parentid = v_parentid;
END;
END LOOP;
CLOSE cr1;
END;
-- Update node's id to its real name.
update_name_label:BEGIN
DECLARE cnt INT DEFAULT 0;
DECLARE i2 INT DEFAULT 0;
SELECT MAX(node_level) FROM tmp_country_list INTO cnt;
WHILE i2 < cnt
DO
UPDATE tmp_country_list AS a, country AS b
SET a.node_path = REPLACE(a.node_path,CONCAT('/',b.id),CONCAT('/',b.name))
WHERE LOCATE(CONCAT('/',b.id),a.node_path) > 0;
SET i2 = i2 + 1;
END WHILE;
END;
SELECT node_path FROM tmp_country_list;
END$$
DELIMITER ;调用结果：
mysql> CALL sp_show_list(); +-----------------------------------------------+ | node_path | +-----------------------------------------------+ | /Earth | | /Earth/North America | | /Earth/South America | | /Earth/Europe | | /Earth/Asia | | /Earth/Africa | | /Earth/Australia | | /Earth/North America/Canada | | /Earth/North America/Central America | | /Earth/North America/Island Nations | | /Earth/North America/United States | | /Earth/North America/United States/Alabama | | /Earth/North America/United States/Alaska | | /Earth/North America/United States/Arizona | | /Earth/North America/United States/Arkansas | | /Earth/North America/United States/California | +-----------------------------------------------+ 16 rows in set (0.04 sec) Query OK, 0 rows affected (0.08 sec) mysql>
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