题解

请你统计各个部门的工资记录数，给出部门编码dept_no、部门名称dept_name以及部门在salaries表里面有多少条记录sum，按照dept_no升序排序

select d.dept_no, d.dept_name, ds.sum
from 
(
    select de.dept_no, count(de.dept_no) as "sum" 
    from salaries as s left join dept_emp as de  --左连接挑出重复的
    on s.emp_no = de.emp_no
    group by de.dept_no  -- 分组统计重复
) as ds
inner join departments as d
on ds.dept_no = d.dept_no
order by d.dept_no;