SQL查询查询

Question

获取至少编写过所有类型书籍的作者列表的SQL查询

表是

      Author_id  |  Author_info  => authors
      Genre_id   |  Genre_info   => genres
      Author_id  |  Genre_id  |  Book_id  => books

我使用Mysql，最好的方法是什么？

Answer 1

如果N是不同类型的数量：

select author_id, count(distinct genre_id) as genres
from books 
group by author_id 
having genres = N

Answer 2

假定数据库架构为

authors
|-  Author_id  -|- Author_info -|
genres
|-  Genre_id   -|- Genre_info  -|
books
|-  Author_id  -|-  Genre_id   -|-  Book_id -|

查询

SELECT authors.Author_id
FROM authors
LEFT INNER JOIN books ON (authors.Author_id = books.Author_id)
GROUP BY authors.Author_id
HAVING COUNT(DISTINCT books.Genre_id) = (SELECT COUNT(*) FROM genres)

Answer 3

试试这个：

SELECT Author_id
FROM books
INNER JOIN Genre USING (Genre)
GROUP BY Author_id
HAVING COUNT(Author_id) >= (SELECT COUNT(*) FROM Genre); 

Answer 4

至少写一本关于所有类型的书

...试

select author_id, count(distinct genre_id) as genres
from books 
group by author_id 
having genres >= 1