题解 | 统计各个部门平均薪资
SELECT
st_t.department,
AVG(ROUND(normal_salary - dock_salary,3)) avg_salary
FROM staff_tb st_t
JOIN salary_tb sa_t ON sa_t.staff_id = st_t.staff_id
WHERE normal_salary - dock_salary BETWEEN 4000 AND 30000
GROUP BY st_t.department
ORDER BY avg_salary DESC
