Select left(学号,4) From Students
create procedure xxk3 as begin select学号,avg(成绩) as 平均成绩 from score group by学号 end
显示出AAA库中每个学生的平均成绩
select month(入学日期) as 入学月份,count(*) as 人数 from students group by month(入学日期)
从students表中分组统计出每个月份入学的学生人数。