simple stock card

Once again this is about my inventory system.

Date              IN        OUT       Balance

                                            20

2003/04/01     5                      25

2003/04/04                 5          20

2003/04/20                 10        10

2003/04/29     3                      13

So, I got 2 recordset

1. rs_stock_receiving (for IN column)
2. rs_stock_issue (for OUT colum)

The sort is from the beginning of the month until end of the month.

I got the first balance column field right but total up the all the same stock code plus all stock receiving minus stock issue

Balance = (addition of all stock which received before the selected month) - (addition of all stock which issued out before the selected month

Problem is to get the first record which is the earliest and loop the 2 tables until end.

So, in this situation, what is the best to do? Many thanks