如何显示学生人数最少的部门的名称

Question

如何编写查询以显示学生人数最少的部门的名称。根据部门名称按升序对结果进行排序

Answer 1

select d.department_name from Department d, Student s where 
d.department_id = s.department_id
group by d.department_name
having count(s.student_id)<=all
(select count(s.student_id) from Department d, Student s where 
d.department_id = s.department_id
group by d.department_name)
order by department_name;

尝试一下。

Answer 2

select d.department_id, d.department_name 
from Department d
join Student s on d.department_id = s.department_id
group by d.department_id
having count(s.student_id) = (select min(count(s2.student_id))
                              from student s2 
                                    join department d2 
                                    on s2.department_id = d2.department_id 
                               group by d2.department_id) 
order by d.department_name

您必须加入2个表才能获得所需信息。

您还必须根据所选信息对它们进行分组，以便您可以对学生进行统计。

最后，你放置条件。需要子查询来检索最少数量的学生。

Answer 3

select d.department_name from 
(select dd.department_name, count(di.department_id) as id from student di
join department dd on di.department_id=dd.department_id group by dd.department_name) d,
(select min(count(*)) as new from student group by department_id) d2
where d.id=d2.new;

Answer 4

select department_name
  from Department
    join Student
     on Department.department_id=Student.department_id
       having count(*) in
        ( select min(count(*)) from Student group by department_id)
        group by Department.department_id,department_name
        order by department_name asc;