题解 | #统计各个部门的工资记录数#

SELECT
    D.dept_no,
    D.dept_name,
    COUNT(S.salary) AS sum
FROM
    salaries AS S
    LEFT JOIN dept_emp AS DE ON DE.emp_no = S.emp_no
    LEFT JOIN departments AS D ON D.dept_no = DE.dept_no
GROUP BY D.dept_no
ORDER BY
    D.dept_no