Question

假设我有发布者的数据库，他们使用作者，撰写图书。

或者用另一种方式来表达，每本图书都是由作者撰写的，他们为发布商工作。

publishers: id
authors: id, publisher_id
books: id, author_id

我知道如何从this question获取每个人都有多少作者的发布商列表。

如何获取每个发布了多少本书的发布商列表？

我如何才能同时获得两个出版商，每个出版商都有作者数量和图书数量？

Answer 1

试试这个

SELECT COUNT(DISTINCT b.`id`) noofbooks,COUNT(DISTINCT au.id) noofauthers,pub.id publisher FROM publisher pub
    INNER JOIN auther au ON au.`pub_id`= pub.`id`
    INNER JOIN books b ON b.`aut_id` = au.`id` GROUP BY pub.id

Answer 2

您需要三个表连接

SELECT publisher.id, count(*) from publisher 
INNER JOIN author on publisher.id = author.publisher_id 
INNER JOIN book on author.id = book.author_id GROUP BY publisher.id;

Answer 3

您只需触发一个简单的SQL连接查询，如下所示。

    SELECT p.publishers , COUNT(a.authors) totalAuthors, COUNT(b.books) TotalBooks
    FROM publishers AS p,authors AS a ,books AS b
    WHERE p.publishersid = a.publishersid
    AND a.authorsid = b.authorsid
    GROUP BY p.publishersid;

Answer 4

我最终得到了类似于bhanu的回答：

SELECT publishers.*,
COUNT(DISTINCT authors.id) AS 'author_count',
COUNT(DISTINCT books.id) AS 'book_count'
FROM publishers
LEFT JOIN authors ON (authors.publisher_id = publishers.id)
LEFT JOIN books ON (books.author_id = authors.id)
GROUP BY publishers.id;

MySQL：如何计算对表的引用的引用？

4 个答案: