What Logic should I use to compare Data for One Month to another ?


My Table contains following fileds.

Accountno N (10) && example 1234567891
Month N (8,2) && 2013.10 represents Jan,2013.91 Represents October
Invoice N (14) & Amount N(10)

I have been asked to compare the Monthly Amounts with the preceding months Amount. Also Compare one year to another.

What logic should I use, How to start up with this.