SELECT需要对PostgreSQL中的一对多表进行多次联接 | SELECT需要对PostgreSQL中的一对多表进行多次联接

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问题描述

玩具示例：此EDR图中显示了一个数据库模式：

Toy example: I have a database schema shown in this EDR diagram:

Student 与 StudyGroup一对多

StudyGroup 与借用

借书与书一对一。

Student one-to-many with StudyGroup
StudyGroup one-to-many with Borrowed
Borrowed one-to-many with Books.

我想获得单个 的所有研究组 借用的所有本书学生。

I want to get all books that have been borrowed by all study groups of a single Student.

+------------+---------+----------------+
| student.id | book.id | study_group.id |
+------------+---------+----------------+
|          1 |       1 |              1 |
|          1 |       2 |              1 |
|          1 |       3 |              1 |
|          1 |       4 |              2 |
|          1 |       1 |              2 |
+------------+---------+----------------+

在这种情况下，我不确定如何构造多个联接

I'm unsure how to construct the multiple joins in this case,

SELECT student.id, book.id, study_group.id
FROM ...
    INNER JOIN...
    INNER JOIN...
WHERE student.id == 1

推荐答案

我建议您阅读

如果您想要显示表格，

SELECT student.id, book.id, study_group.id
FROM student
    INNER JOIN study_group on (student.id = study_group.student_id)
    INNER JOIN borrowed on (study_group.id = borrowed.group_id)
    INNER JOIN book on (borrowed.book_id = book.id)
WHERE student.id == 1

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