On Wed, Jun 01, 2005 at 18:00:49 +0200, Alain Reymond <[EMAIL PROTECTED]> wrote: > Hello, > > I have the following problem : > > I have a table like > Id Num Date AValue > 1 10 01/01/2005 50 > 2 10 31/05/2005 60 > 3 25 02/02/2005 55 > 4 25 15/03/2005 43 > 5 25 28/05/2005 62 > etc.. > > Id is unique, Num is an identification number with duplicates possible, > date is a ... date and Avalue... a value! > > If we have > Id Num Date AValue > Id1 Num1 Date1 AValue1 > Id2 Num1 Date2 AValue2 > > The table is ordered on Num+Date. > What I would like to calculate is (AValue2-AValue1) for a given Num > (here num1). > > In this case, I would have to calculate > 60-50 for Num 10 > and > 43-55, 62-43 for Num 25. > > Do you have any idea if it can be done simply with a request...
I would suggest using a different design. Probably the easiest is to put the start and end dates and values in one record. Otherwise you could write a function or have your application read entries for a particular Num value ordered by date and treat them as pairs. If any intervals overlap then there really isn't a fix. ---------------------------(end of broadcast)--------------------------- TIP 8: explain analyze is your friend
