我正在尝试进行查询,返回书籍中的书名、书籍摘要和作者姓名,其中只有一位作者按书籍 ID 排序。一本书可以有很多作者,一个作者可以写很多书,所以这是多对多的关系,但是我做错了什么或者忘记了什么。
我的表是:
book_tb(id, title, summary);
author_tb(id, name);
book_author_tb(id, book_id, author_id);
我试过:
SELECT b.title, b.summary, a.name
FROM book_tb b
INNER JOIN book_author_tb ba ON b.id = ba.book_id
INNER JOIN author_tb a ON ba.author_id = a.id
GROUP BY b.title, b.summary, a.name, b.id
HAVING count(ba.author_id) = 1
ORDER BY b.id;
最佳答案
一种方法是:
SELECT b.title, b.summary, a.name
FROM book_author_tb ba
INNER JOIN book_tb b ON b.id = ba.book_id
INNER JOIN author_tb a ON a.id = ba.author_id
WHERE (
SELECT COUNT(*)
FROM book_author_tb
WHERE book_id = b.id
) = 1
ORDER BY b.id
这个:
SELECT COUNT(*) FROM book_author_tb WHERE book_id = b.id
确保返回的书籍只有一位作者。
另一种方式(可能更有效):
SELECT b.title, b.summary, a.name
FROM (
SELECT book_id, MAX(author_id) author_id
FROM book_author_tb
GROUP BY book_id
HAVING COUNT(*) = 1
) ba
INNER JOIN book_tb b ON b.id = ba.book_id
INNER JOIN author_tb a ON a.id = ba.author_id
ORDER BY b.id
关于sql - Postgres 查询返回只有一位作者的书籍,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/56306996/