题解 | #统计各个部门的工资记录数#

/*
#先查询记录
select count(*) as 'sum'
FROM salaries as s
left join dept_emp as de
on s.emp_no = de.emp_no
WHERE dept_no is not NULL
GROUP by dept_no
*/
select depart.dept_no, depart.dept_name, fir.s as 'sum'
FROM departments as depart
join (select dept_no, count(*) as s
FROM salaries as s
left join dept_emp as de
on s.emp_no = de.emp_no
WHERE dept_no is not NULL
GROUP by dept_no) as fir
on depart.dept_no = fir.dept_no
ORDER by dept_no;