乐趣区

关于mysql:聊聊mysql的树形结构存储及查询

本文次要钻研一下 mysql 的树形构造存储及查问

存储 parent

这种形式就是每个节点存储本人的 parent_id 信息

  • 建表及数据筹备

    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);
  • 查问

    -- 查问跟节点下的所有节点
    SELECT t1.name AS lev1, t2.name as lev2, t3.name as lev3
    FROM menu AS t1
    LEFT JOIN menu AS t2 ON t2.parent_id = t1.id
    LEFT JOIN menu AS t3 ON t3.parent_id = t2.id
    WHERE t1.name = 'level1a';
    
    +---------+------------+-------------+
    | lev1    | lev2       | lev3        |
    +---------+------------+-------------+
    | level1a | level2a-1a | level3-2a1a |
    | level1a | level2b-1a | level3-2b1a |
    +---------+------------+-------------+
    
    -- 查问叶子节点
    SELECT t1.name FROM
    menu AS t1 LEFT JOIN menu as t2
    ON t1.id = t2.parent_id
    WHERE t2.id IS NULL;
    
    +-------------+
    | name        |
    +-------------+
    | level3-2a1a |
    | level3-2b1a |
    | level3-2a1b |
    | level3-2b1b |
    +-------------+

    存储及批改上比拟不便,就是要在 sql 外头查问树比拟吃力,个别是加载到内存由利用本人结构

存储 path

这种形式在存储 parent 的根底上,额定存储 path,即从根节点到该节点的门路

  • 建表及数据筹备

    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');
  • 查问

    -- 查问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拟方面,就是批改比拟吃力,特地是节点挪动,所有子节点的 path 都得跟着批改

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程序决定

  • 建表及数据筹备

    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)13
    3(level3a-2a)4 5(level3b-2a)6 9(level3c-2b)10 11(level3d-2b)12
    
    INSERT 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  |
    +----+------------+-----+-----+
  • 查问

    -- 查问某个节点及其子节点,比方 level2b
    select * 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  |
    +----+------------+-----+-----+
    
    -- 查问所有叶子节点
    SELECT name
    FROM menu_preorder
    WHERE rgt = lft + 1;
    
    +------------+
    | name       |
    +------------+
    | level3a-2a |
    | level3b-2a |
    | level3c-2b |
    | level3d-2b |
    +------------+
    
    -- 查问某个节点及其父节点
    SELECT parent.*
    FROM menu_preorder AS node,
    menu_preorder AS parent
    WHERE node.lft BETWEEN parent.lft AND parent.rgt
    AND node.name = 'level2b'
    ORDER BY parent.lft;
    
    +----+---------+-----+-----+
    | id | name    | lft | rgt |
    +----+---------+-----+-----+
    | 1  | level1a | 1   | 14  |
    | 3  | level2b | 8   | 13  |
    +----+---------+-----+-----+
    
    -- 树形构造展现
    SELECT CONCAT(REPEAT(' ', COUNT(parent.name) - 1), node.name) AS name
    FROM menu_preorder AS node,
    menu_preorder AS parent
    WHERE node.lft BETWEEN parent.lft AND parent.rgt
    GROUP BY node.name
    ORDER BY node.lft;
    
    +--------------+
    | name         |
    +--------------+
    | level1a      |
    |  level2a     |
    |   level3a-2a |
    |   level3b-2a |
    |  level2b     |
    |   level3c-2b |
    |   level3d-2b |
    +--------------+

益处是通过 lft 进行范畴 (该节点的 lft,rgt 作为范畴) 查找就能够,毛病就是增删节点导致很多节点的 lft 及 rgt 都要批改

小结

  • 存储 parent 的形式最为场景,个别树形构造数据量不大的话,间接在应用层内存结构树形构造和搜寻
  • 存储 path 的益处是能够借助 path 来查找节点及其子节点,毛病就是挪动 node 须要级联所有子节点的 path,比拟吃力
  • MPTT 的形式益处是通过 lft 进行范畴 (该节点的 lft,rgt 作为范畴) 查找就能够,毛病就是增删节点导致很多节点的 lft 及 rgt 都要批改

doc

  • Managing Hierarchical Data in MySQL
  • hierarchical-data-database
  • hierarchical-data-database-2
  • hierarchical-data-database-3
退出移动版