计算属于类别及其子类别的所有帖子 [英] Counting all the posts belonging to a category AND its subcategories

问题描述

我真的很感谢我的问题的一些帮助：

I would really appreciate some help with my problem:

我有2个MySQL表，类别和帖子，布局（简化）如下：

I have 2 MySQL tables, categories and posts, laid out (simplified) like so:

类别：

CATID - name - parent_id

CATID - name - parent_id

帖子：

PID - 名称 - 类别

PID - name - category

我想做的是获得每个类别的帖子总数，包括子类别中的任何帖子。

What I would like to do is get the total amount of posts for each category, including any posts in subcategories.

现在我得到每个类别中的总帖子数顶部级别）类别（但不是子类别）：

Right now I am getting the total number of posts in each (top-level) category (but not subcategories) by doing:

"SELECT c.*, COUNT(p.PID) as postCount 
        FROM categories AS c LEFT JOIN posts AS p 
        ON (c.CATID = p.category) 
        WHERE c.parent='0' GROUP BY c.CATID ORDER BY c.name ASC"; 

问题再次是，如何获得每个类别的总计

The question once again is, how can I get the sum totals for each category including the totals for each related subcategory?

由于我维护现有系统，因此无法将数据库重组为嵌套集格式。

Restructuring the database to a nested set format is not possible, as I am maintaining an existing system.

感谢您的帮助！

推荐答案

如果类别不是无限嵌套，一次加入一个级别。以下是最多3层嵌套的示例：

If the categories are not nested infinitely, you can JOIN them one level at a time. Here's an example for up to 3 levels of nesting:

SELECT c.name, COUNT(DISTINCT p.PID) as postCount 
FROM categories AS c 
LEFT JOIN categories AS c2
    ON c2.parent = c.catid
LEFT JOIN categories AS c3
    ON c3.parent = c2.catid
LEFT JOIN posts AS p 
    ON c.CATID = p.category
    OR c2.CATID = p.category
    OR c3.CATID = p.category
WHERE c.parent = '0' 
GROUP BY c.CATID, c.name
ORDER BY c.name ASC

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