>I have fields :

>
>sid      total    student_number  rank
>
>1         100            99               1
>2         100            90               2
>3          100           90               2
>4           100           70              3
>....
>I want to update student ranks in my table

What is your database? In SQL Server you can use DENSE_RANK() function. In VFP you need two steps:

create cursor Ranks (Rank I autoinc, Student_Number I)

insert into Ranks (Student_Number) select Distinct Student_Number from StudentScores ORDER BY Student_Number DESC

Update S set Rank = Ranks.Rank from StudentScores S inner join Ranks on S.Student_Number = Ranks.Student_Number