sql在两个表中找到最大相同主题

Question

Q值。让部门的规模是教师的数量加上学生的数量。找到最大部门的名称。

select dept_name
from(select dept_name,count(id) as people from instructor group by dept_name
union
select dept_name,count(id) as people from student group by dept_name)
having count(id)=(select max(A.people)
                  from (select count(id) as people
                        from (select dept_name,count(id) as people 
                        from instructor 
                        group by dept_name
                        union
                        select dept_name,count(id) as people 
                        from student 
                        group by dept_name)
                        group by dept_name) as A)

讲师表视图：

学生表视图：

[在此输入图像说明] [3]

结果是Comp.Sci。

Answer 1

SELECT COUNT(*) + 
(SELECT COUNT(*) FROM student where dept_name = t1.dept_name) as total_member,
t1.dept_name FROM instructor 
GROUP BY t1.dept_name 
ORDER BY total_member DESC
LIMIT 1

Answer 2

我测试了我的测试样本数据库并且它有效！

它也适合你。要包含重复记录，您可以考虑使用UNION ALL，如下所示：

SELECT MAX(total),dept_name 
FROM (
SELECT count(a.dept_name) as total,a.dept_name 
from student a left join instructor b ON a.dept_name = b.dept_name GROUP BY a.dept_name
union all select count(c.dept_name) as total,c.dept_name
from instructor c RIGHT JOIN student d ON  c.dept_name = d.dept_name group by c.dept_name) combine_table

Answer 3

  select top 1 dept_name from
(
  select dept_name, sum(student_num + inst_num)
    from(
    select dept_name, 0 as student_num, count(id) as inst_num from instructor group by dept_name
        union all
    select dept_name,count(id) as student_num, 0 as inst_num from student group by dept_name
    )t group by t.dept_name
    order by sum(student_num + inst_num) desc
)