关于集函数的问题？

Question

CREATE PROCEDURE  jCountAverage_Proc @Classid char(8) ,@Term char(5) AS
declare @tsum float
select @Tsum=sum(CreditHour)
 from ClassSchedule 
where ClassNo=@Classid and term=@Term
select sum(Single)/@Tsum,StudentNo  
from Achievement 
where ClassNo=@Classid and term=@Term
group by StudentNo
go

Answer 1

对
Achievement.StudentNo
Achievement.ClassNo
Achievement.term
ClassSchedul.ClassNo
ClassSchedul.term
加索引