mysql - MYSQL查询通过多层一对多关系

Question

如何从许多一对多关系中选择所有事物，在许多一对多关系中向下几层？我不确定如何嵌套所有左连接。

例子

There are many Institutions
Each Institution has many Departments
Each Department has many Forums
Each Forum has many Users
Each User has many Posts
Each Post has many Comments

查找机构的所有评论。

我四处搜索，但我不确定它的名称是什么 - 链嵌套的一对多关系查询？我发现的最接近的是SQL 左连接与 FROM 行上的多个表？

Answer 1

在不知道您的架构并做出一些假设的情况下：

SELECT c.*
FROM
    Institution i
    INNER JOIN Department d ON d.InstitutionID = i.InstitutionID
    INNER JOIN Forums f ON f.DepartmentID = d.DepartmentID
    INNER JOIN `User` u ON u.ForumID = f.ForumID
    INNER JOIN Post p ON p.UserID = u.UserID
    INNER JOIN Comment c ON c.PostID = p.PostID
WHERE
    i.InstitutionID = 42