create view view2(sno,savg,sname)
as select Student.Sno,Sname,AVG((cast(StudentCourse.Grade as int)))
from Student join StudentCourse
on StudentCourse.Sno=Student.Sno
group by Student.Sno,Student.Sname
即可，反正Sno已经保证唯一了，再加上Sname也无法再干扰什么了。
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