Question

我有下一个输入数据，有两个表

create table Courses(
id number(19) not null,
name varchar(100),
);

create table Students (
id number (19) not null,
name varchar(100),
course_id number (19) not null,
);

我需要编写查询以获取具有学生数量的所有cource，例如超过10 所以，我用这样的嵌套查询编写了变体

select distinct courses.name from student, courses where courses.id=student.courses_id and (select count(Students.id) from Students where student.course_id = course.id)  > 10

!!!没有测试，只为这篇文章写的，这是例子!!! 所以，我的问题是如何在没有嵌套查询的情况下编写相同的查询？

Answer 1

使用GROUP BY / HAVING子句：

SELECT courses.name /*, COUNT(*)*/
FROM student JOIN courses ON courses.id = student.courses_id
GROUP BY courses.id
HAVING COUNT(*) > 10

Answer 2

我会选择

Select c.name, count(s.id) as StudentsCount from Courses c join stundets S on c.id = s.course_id group by c.name having count(s.id) > 10

SQL：选择没有嵌套查询的查询

2 个答案: