Question

我有一个Student表，其中的列如下：

| email (PK) | name |

我有一张带有栏目的书桌：

| bookid(PK) | title |

我有一个副本表，其中包含人们拥有的图书副本

| emailofOwner(FK to student.email) | bookid(FK to book.bookid) |

学生当然可以拥有多本书。我的目的是找到只拥有1本书的学生的名字而没有其他但只有bookid = 3;

我试图让那些只拥有一本书的人。

select c.emailofOwner
from copy c
group by c.emailofOwner
having count(*) = 1 ;

Answer 1

SELECT t1.name
FROM student t1
INNER JOIN
(
    SELECT emailofOwner
    FROM copy
    GROUP BY emailofOwner
    HAVING COUNT(DISTINCT bookid) = 1 AND MAX(bookid) = 3
) t2
    ON t1.email = t2.emailofOwner

上述查询使用子查询来限制拥有一本且只有一本ID为3的图书的学生。子查询与您的尝试相同，只是它添加了最大书籍ID为3的限制。在这种情况下，由于每个保留组只有一本书，这只是检查书籍ID的值。

Answer 2

仅限学生

select s.name, s.email, count(*) as numBooks
from student s, copy c
where s.email = c.emailOfOwner
group by email
having count(*) = 1

有书3的人只能预订3：

select s.name, s.email, count(*) as numBooks
from student s, copy c
where s.email = c.emailOfOwner
group by email
having count(*) = 1 and min(bookId) = 3;

查看此SQL Fiddle。

SQL：获取一位特定的图书所有者

2 个答案: