I have a student.dbf having fields 1. Regno 2.name 3. Maths 4. Physics 5.Chemistry 6.Total 7. dob 8. category 9. Rank 10. MBC rank 11. sc rank.

I have two types of category field namely 1.MBC 2.SC

I want to put the rank based on the total marks field in Rank field and also put the category field rank in MBC field and SC field

How to write the source code?