Calculating difference from previous record - sql

Question

May I ask for your help with the following please ?
I am trying to calculate a change from one record to the next in my results. It will probably help if I show you my current query and results ...
SELECT A.AuditDate, COUNT(A.NickName) as [TAccounts],
SUM(IIF((A.CurrGBP > 100 OR A.CurrUSD > 100), 1, 0)) as [Funded]
FROM Audits A
GROUP BY A.AuditDate;
The query gives me these results ...
AuditDate D/M/Y TAccounts Funded
--------------------------------------------
30/12/2011 506 285
04/01/2012 514 287
05/01/2012 514 288
06/01/2012 516 288
09/01/2012 520 289
10/01/2012 522 289
11/01/2012 523 290
12/01/2012 524 290
13/01/2012 526 291
17/01/2012 531 292
18/01/2012 532 292
19/01/2012 533 293
20/01/2012 537 295
Ideally, the results I would like to get, would be similar to the following ...
AuditDate D/M/Y TAccounts TChange Funded FChange
------------------------------------------------------------------------
30/12/2011 506 0 285 0
04/01/2012 514 8 287 2
05/01/2012 514 0 288 1
06/01/2012 516 2 288 0
09/01/2012 520 4 289 1
10/01/2012 522 2 289 0
11/01/2012 523 1 290 1
12/01/2012 524 1 290 0
13/01/2012 526 2 291 1
17/01/2012 531 5 292 1
18/01/2012 532 1 292 0
19/01/2012 533 1 293 1
20/01/2012 537 4 295 2
Looking at the row for '17/01/2012', 'TChange' has a value of 5 as the 'TAccounts' has increased from previous 526 to 531. And the 'FChange' would be based on the 'Funded' field. I guess something to be aware of is the fact that the previous row to this example, is dated '13/01/2012'. What I mean is, there are some days where I have no data (for example over weekends).
I think I need to use a SubQuery but I am really struggling to figure out where to start. Could you show me how to get the results I need please ?
I am using MS Access 2010
Many thanks for your time.
Johnny.

Answer 1

Here is one approach you could try...
SELECT B.AuditDate,B.TAccounts,
B.TAccount -
(SELECT Count(NickName) FROM Audits WHERE AuditDate=B.PrevAuditDate) as TChange,
B.Funded -
(SELECT Count(*) FROM Audits WHERE AuditDate=B.PrevAuditDate AND (CurrGBP > 100 OR CurrUSD > 100)) as FChange
FROM (
SELECT A.AuditDate,
(SELECT Count(NickName) FROM Audits WHERE AuditDate=A.AuditDate) as TAccounts,
(SELECT Count(*) FROM Audits WHERE (CurrGBP > 100 OR CurrUSD > 100)) as Funded,
(SELECT Max(AuditDate) FROM Audits WHERE AuditDate<A.AuditDate) as PrevAuditDate
FROM
(SELECT DISTINCT AuditDate FROM Audits) AS A) AS B
Instead of using a Group By I've used subquerys to get both TAccounts and Funded, as well as the Previous Audit Date, which is then used on the main SELECT statement to get TAccounts and Funded again but this time for the previous date, so that any required calculation can be done against them.
But I would imagine this may be slow to process

Answer 2

It's a shame MS never made this type of thing simple in Access, how many rows are you working with on your report?
If it's under 65K then I would suggest dumping the data on to an Excel spreadsheet and using a simple formula to calculate the different between rows.

Answer 3

You can try something like the following (sql is untested and will require some changes)
SELECT
A.AuditDate,
A.TAccounts,
A.TAccounts - B.TAccounts AS TChange,
A.Funded,
A.Funded - B.Funded AS FChange
FROM
( SELECT
ROW_NUMBER() OVER (ORDER BY AuditDate DESC) AS ROW,
AuditDate,
COUNT(NickName) as [TAccounts],
SUM(IIF((CurrGBP > 100 OR CurrUSD > 100), 1, 0)) as [Funded]
FROM Audits
GROUP BY AuditDate
) A
INNER JOIN
( SELECT
ROW_NUMBER() OVER (ORDER BY AuditDate DESC) AS ROW,
AuditDate,
COUNT(NickName) as [TAccounts],
SUM(IIF((CurrGBP > 100 OR CurrUSD > 100), 1, 0)) as [Funded]
FROM Audits
GROUP BY AuditDate
) B ON B.ROW = A.ROW + 1