计算属于一个类别及其子类别的所有帖子
我真的很感激能帮助我解决我的问题:
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 - 名称 - parent_id
CATID - name - parent_id
帖子:
PID - 名称 - 类别
PID - name - category
我想要做的是获取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.
现在我通过执行以下操作获得每个(顶级)类别(但不是子类别)中的帖子总数:
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和，包括每个相关子类别的总和?
无法将数据库重构为嵌套集格式，因为我正在维护现有系统.
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的，您可以一次加入一层.以下是最多 3 级嵌套的示例:
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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