Question

select substring(学号,1,2) as 年级,avg(成绩) as 平均成绩 from group by substring(学号,1,2)

select substring(学号,1,2) as 年级,avg(成绩) as 平均成绩 from group by substring(学号,1,2) 到底是什么意思啊？？

Answer 1

substring(学号,1,2) 截取学号的前两位作为年级

group by substring(学号,1,2)

按年级分组，求出每个年级的平均成绩 avg(成绩) 。