题解 | #统计各个部门的工资记录数#

select 
t1.dept_no,
t1.dept_name,
count(*) as sum
from 
        (select dept_no, dept_name
        from departments) as t1
    left join
        (select emp_no, dept_no
        from dept_emp)as t2
        on t1.dept_no = t2.dept_no
    left join 
        (select salary, emp_no
        from salaries) as t3
        on t3.emp_no = t2.emp_no 
group by t1.dept_no,t1.dept_name

主打一个使劲连