>>Try UPDATE-SQL command
>>
>>

>>update Res SET Grade = ICASE(BETWEEN(Perc, 80,100), 'A+', Perc >= 70, 'A',...)

>>
>>What do you want for the case when Perc > 100 ?
>

i want use only PERC<=100

I would account for this case (even if it never happens) and start from it, e.g.

ICASE(Perc > 100, 'O', Perc >=80,'A+', Perc >= 70, 'A', Perc >='65', 'B+', Perc >=60, 'B', etc.)