MySQL的分层数据管理、无限级分类、设计与优化_MySQL

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MySQL的分层数据管理、无限级分类、设计与优化

1.文章里介绍了常见的基于parent_id的邻接表模型:

  CREATE TABLE category(      category_id INT AUTO_INCREMENT PRIMARY KEY,      name VARCHAR(20) NOT NULL,      parent INT DEFAULT NULL    );    +-------------+----------------------+--------+    | category_id | name                 | parent |    +-------------+----------------------+--------+    |           1 | ELECTRONICS          |   NULL |    |           2 | TELEVISIONS          |      1 |    |           3 | TUBE                 |      2 |    |           4 | LCD                  |      2 |    |           5 | PLASMA               |      2 |    |           6 | PORTABLE ELECTRONICS |      1 |    |           7 | MP3 PLAYERS          |      6 |    |           8 | FLASH                |      7 |    |           9 | CD PLAYERS           |      6 |    |          10 | 2 WAY RADIOS         |      6 |    +-------------+----------------------+--------+

和基于"先序遍历算法"的嵌套集合(Nested Set)模型:

CREATE TABLE nested_category (      category_id INT AUTO_INCREMENT PRIMARY KEY,      name VARCHAR(20) NOT NULL,      lft INT NOT NULL,      rgt INT NOT NULL    );    +-------------+----------------------+-----+-----+    | category_id | name                 | lft | rgt |    +-------------+----------------------+-----+-----+    |           1 | ELECTRONICS          |   1 |  20 |    |           2 | TELEVISIONS          |   2 |   9 |    |           3 | TUBE                 |   3 |   4 |    |           4 | LCD                  |   5 |   6 |    |           5 | PLASMA               |   7 |   8 |    |           6 | PORTABLE ELECTRONICS |  10 |  19 |    |           7 | MP3 PLAYERS          |  11 |  14 |    |           8 | FLASH                |  12 |  13 |    |           9 | CD PLAYERS           |  15 |  16 |    |          10 | 2 WAY RADIOS         |  17 |  18 |    +-------------+----------------------+-----+-----+

2.分析与点评

上述两种算法我个人觉得各和优点,在页面上的类目,在web网站里,最常见的场景是

1."检索节点的直接子节点"

2."检索完整的子树"

场景PK:

1."检索节点的直接子节点"

就是查找一个目录的直接下级元素,如查询'PORTABLE ELECTRONICS'的直接下级元素:

对于"基于parent_id的邻接表模型",直接

    "SELECT id,name FROM category WHERE parent_id = 6;"

查找特定parent_id的所有元素就可以了.

对于"嵌套集合(Nested Set)模型",按原文的方法可复杂了:

    SELECT node.name, (COUNT(parent.name) - (sub_tree.depth + 1)) AS depth         FROM nested_category AS node,        nested_category AS parent,               nested_category AS sub_parent,        (        SELECT node.name, (COUNT(parent.name) - 1) AS depth        FROM nested_category AS node,        nested_category AS parent        WHERE node.lft BETWEEN parent.lft AND parent.rgt        AND node.name = 'PORTABLE ELECTRONICS'        GROUP BY node.name        ORDER BY node.lft        )AS sub_tree         WHERE node.lft BETWEEN parent.lft AND parent.rgt        AND node.lft BETWEEN sub_parent.lft AND sub_parent.rgt        AND sub_parent.name = sub_tree.name         GROUP BY noe.name         HAVING depth 
 
    这可是最常见的场景,我相信"嵌套集合"这里的性能不会很好,这里"邻接表模型"性能好很多!　
 
 
 2."检索完整的子树"
       如查询以"PORTABLE ELECTRONICS"为根的子树
       对于"基于parent_id的邻接表模型",很复杂,涉及到递归操作,用客户端代码会很复杂,用存储过程还是一样递归搜索,性能实在不行. 
 
       对于"嵌套集合(Nested Set)模型",相当简单:
      
  "SELECT id,name,parent_id FROM category WHERE lft BETWEEN 10 AND 19 ORDER BY lft" 
 
   这里"嵌套集合模型"性能好很多!
 
3.无限级分类优化　 　
 
　能不能整合"邻接表模型"和"嵌套集合模型"呢？我们试试看　
 
    CREATE TABLE category (      id INT AUTO_INCREMENT PRIMARY KEY,      name VARCHAR(20) NOT NULL,      lft INT NOT NULL,      rgt INT NOT NULL,      parent_id INT    );
 
 
    表面看上去只是简单的数据整合,实际上述两种模式的功能都整合起来了,
    对于1."检索节点的直接子节点"的场景(利用"邻接表模型"的特性):         "SELECT id,name FROM category WHERE parent_id = 6;"         对于2."检索完整的子树"场景(利用"嵌套集合模型"的特性):　    "SELECT id,name,parent_id FROM category WHERE lft BETWEEN 10 AND 19;"
 
 
    这是"邻接表-嵌套集合-混合模型",
    相对于"嵌套集合模型",只是简单地增加了"parent_id"字段,就获得了"邻接表模型"的优点,邻接表与嵌套集合的优点整合,非常不错呢
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