题解 | 统计各岗位员工平均工作时长

SELECT post,
ROUND((SUM(w_hour) / COUNT(w_hour)) , 3) AS work_hours
FROM staff_tb AS s
LEFT JOIN 
    (SELECT staff_id,
    TIMESTAMPDIFF(minute,first_clockin,last_clockin)/60 AS w_hour
    FROM attendent_tb) AS b
ON s.staff_id = b.staff_id
GROUP BY post
ORDER BY work_hours DESC

#难点：有部分员工未打卡，计算员工数时需注意COUNT(w_hour)