mysql的树形结构存储及查询实例分析

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存储parent

这种方式就是每个节点存储自己的parent_id信息

• 建表及数据准备

CREATE TABLE `menu` (  `id` int(11) NOT NULL AUTO_INCREMENT,  `name` varchar(50) NOT NULL,  `parent_id` int(11) NOT NULL DEFAULT '0',  PRIMARY KEY (`id`)) ENGINE=InnoDB;INSERT INTO `menu` (`id`, `name`, `parent_id`) VALUES(1, 'level1a',  0),(2, 'level1b', 0),(3, 'level2a-1a',1),(4, 'level2b-1a',1),(5, 'level2a-1b', 2),(6, 'level2b-1b', 2),(7, 'level3-2a1a', 3),(8, 'level3-2b1a', 4),(9, 'level3-2a1b', 5),(10, 'level3-2b1b', 6);

• 查询

-- 查询跟节点下的所有节点SELECT t1.name AS lev1, t2.name as lev2, t3.name as lev3FROM menu AS t1LEFT JOIN menu AS t2 ON t2.parent_id = t1.idLEFT JOIN menu AS t3 ON t3.parent_id = t2.idWHERE t1.name = 'level1a';+---------+------------+-------------+| lev1    | lev2       | lev3        |+---------+------------+-------------+| level1a | level2a-1a | level3-2a1a || level1a | level2b-1a | level3-2b1a |+---------+------------+-------------+-- 查询叶子节点SELECT t1.name FROMmenu AS t1 LEFT JOIN menu as t2ON t1.id = t2.parent_idWHERE t2.id IS NULL;+-------------+| name        |+-------------+| level3-2a1a || level3-2b1a || level3-2a1b || level3-2b1b |+-------------+

存储及修改上比较方便，就是要在sql里头查询树比较费劲，一般是加载到内存由应用自己构造

存储path

这种方式在存储parent的基础上，额外存储path，即从根节点到该节点的路径

• 建表及数据准备

CREATE TABLE `menu_path` (  `id` int(11) NOT NULL AUTO_INCREMENT,  `name` varchar(50) NOT NULL,  `parent_id` int(11) NOT NULL DEFAULT '0',  `path` varchar(255) NOT NULL DEFAULT '',  PRIMARY KEY (`id`)) ENGINE=InnoDB;INSERT INTO `menu_path` (`id`, `name`, `parent_id`, `path`) VALUES(1, 'level1a', 0, '1/'),(2, 'level1b', 0, '2/'),(3, 'level2a-1a',1, '1/3'),(4, 'level2b-1a',1, '1/4'),(5, 'level2a-1b', 2, '2/5'),(6, 'level2b-1b', 2, '2/6'),(7, 'level3-2a1a', 3, '1/3/7'),(8, 'level3-2b1a', 4, '1/4/8'),(9, 'level3-2a1b', 5, '2/5/9'),(10, 'level3-2b1b', 6, '2/6/10');

• 查询

-- 查询某个节点的所有子节点select * from menu_path where path like '1/%'+----+-------------+-----------+-------+| id | name        | parent_id | path  |+----+-------------+-----------+-------+| 1  | level1a     | 0         | 1/    || 3  | level2a-1a  | 1         | 1/3   || 4  | level2b-1a  | 1         | 1/4   || 7  | level3-2a1a | 3         | 1/3/7 || 8  | level3-2b1a | 4         | 1/4/8 |+----+-------------+-----------+-------+

查找某个节点及其子节点比较方面，就是修改比较费劲，特别是节点移动，所有子节点的path都得跟着修改

MPTT(Modified Preorder Tree Traversal)

不存储parent_id，改为存储lft,rgt，它们的值由树的先序遍历顺序决定

• 建表及数据准备

CREATE TABLE `menu_preorder` (  `id` int(11) NOT NULL,  `name` varchar(50) NOT NULL,  `lft` int(11) NOT NULL DEFAULT '0',  `rgt` int(11) NOT NULL DEFAULT '0',  PRIMARY KEY (`id`)) ENGINE=InnoDB;                   1(level1a)14         2(level2a)7                8(level2b)133(level3a-2a)4 5(level3b-2a)6 9(level3c-2b)10 11(level3d-2b)12INSERT INTO `menu_preorder` (`id`, `name`, `lft`, `rgt`) VALUES(1, 'level1a', 1, 14),(2, 'level2a',2, 7),(3, 'level2b',8, 13),(4, 'level3a-2a', 3, 4),(5, 'level3b-2a', 5, 6),(6, 'level3c-2b', 9, 10),(7, 'level3d-2b', 11, 12);select * from menu_preorder+----+------------+-----+-----+| id | name       | lft | rgt |+----+------------+-----+-----+| 1  | level1a    | 1   | 14  || 2  | level2a    | 2   | 7   || 3  | level2b    | 8   | 13  || 4  | level3a-2a | 3   | 4   || 5  | level3b-2a | 5   | 6   || 6  | level3c-2b | 9   | 10  || 7  | level3d-2b | 11  | 12  |+----+------------+-----+-----+

• 查询

-- 查询某个节点及其子节点，比如level2bselect * from menu_preorder where lft between 8 and 13+----+------------+-----+-----+| id | name       | lft | rgt |+----+------------+-----+-----+| 3  | level2b    | 8   | 13  || 6  | level3c-2b | 9   | 10  || 7  | level3d-2b | 11  | 12  |+----+------------+-----+-----+-- 查询所有叶子节点SELECT nameFROM menu_preorderWHERE rgt = lft + 1;+------------+| name       |+------------+| level3a-2a || level3b-2a || level3c-2b || level3d-2b |+------------+-- 查询某个节点及其父节点SELECT parent.*FROM menu_preorder AS node,menu_preorder AS parentWHERE node.lft BETWEEN parent.lft AND parent.rgtAND node.name = 'level2b'ORDER BY parent.lft;+----+---------+-----+-----+| id | name    | lft | rgt |+----+---------+-----+-----+| 1  | level1a | 1   | 14  || 3  | level2b | 8   | 13  |+----+---------+-----+-----+-- 树形结构展示SELECT CONCAT( REPEAT(' ', COUNT(parent.name) - 1), node.name) AS nameFROM menu_preorder AS node,menu_preorder AS parentWHERE node.lft BETWEEN parent.lft AND parent.rgtGROUP BY node.nameORDER BY node.lft;+--------------+| name         |+--------------+| level1a      ||  level2a     ||   level3a-2a ||   level3b-2a ||  level2b     ||   level3c-2b ||   level3d-2b |+--------------+

好处是通过lft进行范围(该节点的lft,rgt作为范围)查找就可以，缺点就是增删节点导致很多节点的lft及rgt都要修改

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