[AccessD] sql to get stock variation

One way would be to put a FK in the record which holds the PK of the previously stored record for a 
given stock.  That requires looking up the previous record before updating the new record but it 
then gives you a dead simple inner join to get the difference between the current and the previous. 
  Just join the table on itself using the PK and that FK.

It is called a "single linked list" when done in code.

John W. Colby
Colby Consulting

Reality is what refuses to go away
when you do not believe in it

On 10/11/2012 1:15 PM, Philippe lelynx wrote:
> 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
>