SQL大厂笔试真题21

1. avg（if语句）表示满足if条件的记录所占比例。
2. concat（ ，'%'）将数值转换为字符串，并且添加%符号。

代码如下：

select department,

concat(round(avg(if(timestampdiff(minute,first_clockin,last_clockin)/60 > 9.5,1,0))*100,1),'%') as ratio from staff_tb join attendent_tb using(staff_id)

group by department

order by ratio desc