i have a table like this:

StockNumber|InventoryName|Year|Month|Adj|iss|piss|Tsfr|return|rdj|rpo|xefr
alb001      clinic1       2010  1     4   5    5   5    6      5   4   10
alb001      Clinic1       2010  2    10  2    2    3    3      4   4   4
alb001      Clinic1       2010  4    11  3   5    77    90     78   9   6
alb001      Clinic1       2010  5    10  2    2    3    3      4   4   4

i want to add a closing balance column which will be

sum(return+rdj+rpo+xefr) - sum(adj+iss+piss+tsfr)

i also want to add the opening balance column which will be the be the closing balance of the previous month. i will then calculate the current months balance as

OpeningBalance + sum(return+rdj+rpo+xefr) - sum(adj+iss+piss+tsfr) = ClosingBalance

NB.The Year and Month columns are floats and also want to change them to date format. i am newbie to sql and crystal reports....i want a query to help me achieve the tasks of developing a report that has the opening and closing balance columns,the opening balance being the previous closing balance.....thank you for your help....