题解 | #统计各个部门的工资记录数#

select de.dept_no,d.dept_name, count(de.dept_no) sum
from dept_emp de
inner join 
salaries s
on de.emp_no=s.emp_no
inner join
departments d
on de.dept_no=d.dept_no
group by de.dept_no
order by de.dept_no

连接三个表，使用inner join