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实现PHP+Mysql无限分类的方法汇总

　　本文标签：PHP,Mysql,无限分类

无限分类是个老话题了，来看看PHP结合Mysql如何实现 。

第一种方法

这种方法是很常见、很传统的一种，先看表结构

表:category
id int 主键,自增
name varchar 分类名称
pid int 父类id，默认0
顶级分类的 pid 默认就是0了 。当我们想取出某个分类的子分类树的时候，基本思路就是递归，当然，出于效率问题不建议每次递归都查询数据库，通常的做法是先讲所有分类取出来，保存到PHP数组里，再进行处理，最后还可以将结果缓存起来以提高下次请求的效率 。

先来构建一个原始数组，这个直接从数据库中拉出来就行：

复制代码 代码如下:

$categories = array(
    array(id=>1,name=>电脑,pid=>0),
    array(id=>2,name=>手机,pid=>0),
    array(id=>3,name=>笔记本,pid=>1),
    array(id=>4,name=>台式机,pid=>1),
    array(id=>5,name=>智能机,pid=>2),
    array(id=>6,name=>功能机,pid=>2),
    array(id=>7,name=>超级本,pid=>3),
    array(id=>8,name=>游戏本,pid=>3),
);

目标是将它转化为下面这种结构

电脑
    笔记本
        超级本
        游戏本
    台式机
手机
    智能机
    功能机
用数组来表示的话，可以增加一个 children 键来存储它的子分类：

复制代码 代码如下:

array(
    //1对应id，方便直接读取
    1 => array(
        id=>1,
        name=>电脑,
        pid=>0,
        children=>array(
            &array(
                id=>3,
                name=>笔记本,
                pid=>1,
                children=>array(
                    //此处省略
                )
            ),
            &array(
                id=>4,
                name=>台式机,
                pid=>1,
                children=>array(
                    //此处省略
                )
            ),
        )
    ),
    //其他分类省略
)

处理过程：

复制代码 代码如下:

$tree = array();
//第一步，将分类id作为数组key,并创建children单元
foreach($categories as $category){
    $tree[$category[id]] = $category;
    $tree[$category[id]][children] = array();
}
//第二部，利用引用，将每个分类添加到父类children数组中，这样一次遍历即可形成树形结构 。
foreach ($tree as $k=>$item) {
    if ($item[pid] != 0) {
        $tree[$item[pid]][children][] = &$tree[$k];
    }
}
print_r($tree);

打印结果如下：

复制代码 代码如下:

Array
(
    [1] => Array
        (
            [id] => 1
            [name] => 电脑
            [pid] => 0
            [children] => Array
                (
                    [0] => Array
                        (
                            [id] => 3
                            [name] => 笔记本
                            [pid] => 1
                            [children] => Array
                                (
                                    [0] => Array
                                        (
                                            [id] => 7
                                            [name] => 超级本
                                            [pid] => 3
                                            [children] => Array
                                                (
                                                )
                                        )
                                    [1] => Array
                                        (
                                            [id] => 8
                                            [name] => 游戏本
                                            [pid] => 3
                                            [children] => Array
                                                (
                                                )
                                        )
                                )
                        )
                    [1] => Array
                        (
                            [id] => 4
                            [name] => 台式机
                            [pid] => 1
                            [children] => Array
                                (
                                )
                        )
                )
        )
    [2] => Array
        (
            [id] => 2
            [name] => 手机
            [pid] => 0
            [children] => Array
                (
                    [0] => Array
                        (
                            [id] => 5
                            [name] => 智能机
                            [pid] => 2
                            [children] => Array
                                (
                                )
                        )
                    [1] => Array
                        (
                            [id] => 6
                            [name] => 功能机
                            [pid] => 2
                            [children] => Array
                                (
                                )
                        )
                )
        )
    [3] => Array
        (
            [id] => 3
            [name] => 笔记本
            [pid] => 1
            [children] => Array
                (
                    [0] => Array
                        (
                            [id] => 7
                            [name] => 超级本
                            [pid] => 3
                            [children] => Array
                                (
                                )
                        )
                    [1] => Array
                        (
                            [id] => 8
                            [name] => 游戏本
                            [pid] => 3
                            [children] => Array
                                (
                                )
                        )
                )
        )
    [4] => Array
        (
            [id] => 4
            [name] => 台式机
            [pid] => 1
            [children] => Array
                (
                )
        )
    [5] => Array
        (
            [id] => 5
            [name] => 智能机
            [pid] => 2
            [children] => Array
                (
                )
        )
    [6] => Array
        (
            [id] => 6
            [name] => 功能机
            [pid] => 2
            [children] => Array
                (
                )
        )
    [7] => Array
        (
            [id] => 7
            [name] => 超级本
            [pid] => 3
            [children] => Array
                (
                )
        )
    [8] => Array
        (
            [id] => 8
            [name] => 游戏本
            [pid] => 3
            [children] => Array
                (
                )
        )
)

优点：关系清楚，修改上下级关系简单 。

缺点：使用PHP处理，如果分类数量庞大，效率也会降低 。

第二种方法

这种方法是在表字段中增加一个path字段：

表:category
id int 主键,自增
name varchar 分类名称
pid int 父类id，默认0
path varchar 路径
示例数据：

id        name        pid        path
1         电脑        0          0
2         手机        0          0
3         笔记本      1          0-1
4         超级本      3          0-1-3
5         游戏本      3          0-1-3
path字段记录了从根分类到上一级父类的路径，用id+-表示 。

这种方式，假设我们要查询电脑下的所有后代分类，只需要一条sql语句：

select id,name,path from category where path like (select concat(path,-,id,%) as path from category where id=1);
结果：

+----+-----------+-------+
| id | name      | path  |
+----+-----------+-------+
| 3  | 笔记本 | 0-1   |
| 4  | 超级本 | 0-1-3 |
| 5  | 游戏本 | 0-1-3 |
+----+-----------+-------+
这种方式也被很多人所采纳，我总结了下：

优点：查询容易，效率高，path字段可以加索引 。

缺点：更新节点关系麻烦，需要更新所有后辈的path字段 。

以上就是本文的全部内容了，两种方式，你喜欢哪种？希望大家能够喜欢 。