题解 | #统计各个部门的工资记录数#

select d.dept_no,d.dept_name,count(s.salary) as sum 
from departments d
inner join dept_emp dp on dp.dept_no=d.dept_no
INNER join salaries s on s.emp_no=dp.emp_no
group by d.dept_no,d.dept_name
ORDER by d.dept_no asc