[AccessD] sql to get stock variation

Hi all,

I need your help regarding a sql query.

I have a table, say STOCK(stock_date, stock_qty)

It records the stock level at the end of each day.

I need to calculate, for each day, the stock variation.

i.e for the day n => stock(n) - stock(n-1)

How would you build such a query??

Regards,

Philippe Pons