MySQL查询图书馆管理系统

Question

我有以下表

成员（memberNo，姓名，年龄），

书（ISBN，书名，作者，出版者，出版年，类别）

借（memberNo，ISBN，日期）

和我期待的答案或线索以下查询

查找成员的瓦时的名字o不止一次借过同一本书。我一直在使用下列但它给我就列名“name”

SELECT member.name 
    FROM member 
    WHERE member.memberNo IN (SELECT borrowed.member_memberNo 
    FROM borrowed 
    WHERE borrowed.book_isbn IN(
    SELECT COUNT(borrowed.book_isbn) as 'countNo' 
    FROM borrowed 
    WHERE 'countNo' >1)); 

非常感谢

！

Answer 1

您可以使用GROUP BY和COUNT来查找成员借用每本书的次数。

SELECT memberNo, isbn, COUNT(*) AS borrow_times 
FROM borrowed 
GROUP BY memberNo, isbn 

然后检查borrow_times > 1找到谁借的同一本书不止一次的：

：

HAVING borrow_times > 1 

将这个变成一个子查询，以便您可以用member表加入吧

SELECT DISTINCT m.name 
FROM member AS m 
JOIN (
    SELECT memberNo, isbn, COUNT(*) AS borrow_times 
    FROM borrowed 
    GROUP BY memberNo, isbn 
    HAVING borrow_times > 1 
) AS b ON m.memberNo = b.memberNo