Question

I have a table of increasing dates (with gaps) and corresponding values

date        | value
01.02.2012  | 10
02.02.2012  | 11
03.02.2012  | 33
07.02.2012  | 34
08.02.2012  | 13

I am looking for table of differences for values between dates, like this:

02.02.2012 - 01.02.2012  | 11 - 10 = +1
03.02.2012 - 02.02.2012  | 33 - 11 = +22
07.02.2012 - 03.02.2012  | 34 - 33 = +1
08.02.2012 - 07.02.2012  | 13 - 34 = -21

Now I am load table into excel and make calculations there, but I have feeling there is a possible way of getting it by use of sql commands inside database. Is there any?

UPD. Actually I use access as database system, but If there is a difference I can switch to one that best fit.

Answer 1

Since I don’t think analytical functions like Lag are available in access you will need to use a correlated subquery:

SELECT  Date,
        Value,
        NextDate,
        NextValue,
        (NextValue - Value) AS ValueDifference,
        DATEDIFF("D", Date, NextDate) AS DateDifference
FROM    (   SELECT  T.Date,
                    T.Value,
                    (   SELECT  TOP 1 Date
                        FROM    LagTest T1
                        WHERE   T1.Date >  T.Date
                        ORDER BY Date
                    ) AS NextDate,
                    (   SELECT  TOP 1 Value
                        FROM    LagTest T1
                        WHERE   T1.Date >  T.Date
                        ORDER BY Date
                    ) AS NextValue
            FROM    LagTest T
        ) AS T