题解 | 统计各个部门的工资记录数

select c.dept_no,c.dept_name,count(a.emp_no) as sum
from (salaries as a 
left join dept_emp as b
on a.emp_no=b.emp_no
left join departments as c
on b.dept_no=c.dept_no)
group by c.dept_no
order by c.dept_no

主要是会卡在这个sum是用count函数来计算，另外不需要去重