SQL for Microsoft Access 2013

Question

I am trying to get a count of customers who return for additional services that takes into account a comparison of assessment scores prior to the service, grouped by the type of Service. (Ultimately, I also want to be able to ignore returns that are within a month of the orginal service, but I'm pretty sure I can get that wrinkle sorted myself)

When counting results for a particular service, it should look at returns to any service type, not just the original service type. (Edit: *It should also look at all future returns, not just the next or the most recent *).

It does not need to be run often, but there are 15000+ lines of data and computational resources are limited by an underpowered machine (this is for a nonprofit organization), so efficiency would be nice but not absolutely needed.

Sample Data

ServiceTable

CustomerID  Service  Date   ScoreBefore

   A    Service1    1/1/2017    1
   A    Service2    1/3/2017    1
   A    Service1    1/1/2018    4
   B    Service3    3/1/2018    3
   B    Service1    6/1/2018    1
   B    Service1    6/2/2018    1
   C    Service2    1/1/2019    4
   C    Service2    6/1/2019    1

Results should be (not taking into account the date padding option):

Service1
  ReturnedWorse 0
  ReturnedSame  2
  ReturnedBetter 1

Service2
  ReturnedWorse 1
  ReturnedSame 0
  ReturnedBetter 1

Service3
  ReturnedWorse 2

So far, I have tried creating make table queries that could then be queried to get the aggregate info, but I am a bit stuck and suspect there may be a better route.

What I have tried:

SELECT CustomerID, Service, Date, ScoreBefore INTO ReturnedWorse
FROM ServiceTable AS FirstStay
WHERE ((((SELECT COUNT(*)
FROM ServiceTable AS SecondStay
WHERE FirstStay.CustomerID=SecondStay.CustomerID
AND
FirstStay.ScoreBefore> SecondStay.ScoreBefore
AND
SecondStay.Date > FirstStay.Date))));

Any help would be greatly appreciated.

Answer 1

This would have been easier to do with window functions, but they are not available in ms-access.

Here is a query that solves my understanding of your question :

• t0 : pick a record in the table (a customer buying a service)
• t1 : pull out the record corresponding to the next time the same customer contracted any service with an INNER JOIN and a correlated subquery (if there is no such record, the initial record is not taken into account)
• compare the score of the previous record to the current one
• group the results by service id

You can see it in action in this db fiddlde . The results are slightly different from your expectation (see my comments)... but they are consistent with the above explanation ; you might want to adapt some of the rules to match your exact expected result, using the same principles.

SELECT
    t0.service,
    SUM(CASE WHEN t1.scorebefore < t0.scorebefore THEN 1 ELSE 0 END) AS ReturnedWorse,
    SUM(CASE WHEN t1.scorebefore = t0.scorebefore THEN 1 ELSE 0 END) AS ReturnedSame,
    SUM(CASE WHEN t1.scorebefore > t0.scorebefore THEN 1 ELSE 0 END) AS ReturnedBetter
FROM 
    mytable t0
    INNER JOIN mytable t1
        ON  t0.customerid = t1.customerid
        AND t0.date < t1.date
        AND NOT EXISTS (
            SELECT 1 
            from mytable 
            WHERE
                customerid = t1.customerid 
                AND date < t1.date
                AND date > t0.date
        )
GROUP BY t0.service

| service  | ReturnedWorse | ReturnedSame | ReturnedBetter |
| -------- | ------------- | ------------ | -------------- |
| Service1 | 0             | 2            | 0              |
| Service2 | 1             | 0            | 1              |
| Service3 | 1             | 0            | 0              |

---

From your comments, I understand that you want to take into account all future returns and not only the next one. This eliminates the need for a correlatead subquery, and actually yields your expected output. See this db fiddle :

SELECT
    t0.service,
    SUM(CASE WHEN t1.scorebefore < t0.scorebefore THEN 1 ELSE 0 END) AS ReturnedWorse,
    SUM(CASE WHEN t1.scorebefore = t0.scorebefore THEN 1 ELSE 0 END) AS ReturnedSame,
    SUM(CASE WHEN t1.scorebefore > t0.scorebefore THEN 1 ELSE 0 END) AS ReturnedBetter
FROM 
    mytable t0
    INNER JOIN mytable t1
        ON  t0.customerid = t1.customerid
        -- AND t0.service = t1.service
        AND t0.date < t1.date
GROUP BY t0.service

| service  | ReturnedWorse | ReturnedSame | ReturnedBetter |
| -------- | ------------- | ------------ | -------------- |
| Service1 | 0             | 2            | 1              |
| Service2 | 1             | 0            | 1              |
| Service3 | 2             | 0            | 0              |