题解 | #统计各个部门的工资记录数#

select
      ds.dept_no,
      dep.dept_name,
      count(dep.dept_name) as sum
from
    departments dep
right join
(select
      de.emp_no,
      de.dept_no
from
    dept_emp de
right join
    salaries sa
on  de.emp_no = sa.emp_no) as ds
on dep.dept_no = ds.dept_no
group by dep.dept_name,ds.dept_no
order by ds.dept_no
#group by dep.dept_name
# select dd.dept_no,dd.dept_name,count(dd.dept_no) as sum
# from (salaries ss left join
# (select ds.dept_no,ds.dept_name,dp.emp_no
# from departments ds right join dept_emp dp on
# ds.dept_no = dp.dept_no) as dd
# on 
# ss.emp_no = dd.emp_no)
# group by dd.dept_no
# order by dd.dept_no

# select de.dept_no,de.dept_name,sa.salary
# from (departments de 
# right join 
# (select de.dept_no,sa.emp_no,sa.salary
# from dept_emp de right join salaries sa on 
# de.emp_no = sa.emp_no) as ds
# on
# de.dept_no = ds.dept_no)