How to run a subquery based on results of a query SQL - sql

Question

I have 2 queries i'd like to run. The idea here is to run a query on the transaction table by the transaction "type". Based on these results, I want to run another query to see the customers last transaction based on a specific type to see if the service ID was the same. If it's not the same, I want to flag it as "upgraded"
Here is the initial query that Pulls the results from a transactions table based on a transaction type:
Select customerid, serviceid
from Transactions
where (dtcreated > #startdate and dtcreated < #enddate) and (transactiontype = 'Cust Save')
The output for this is:
Customerid ServiceID
1 11
2 21
3 21
4 11
5 12
6 11
What i'd like to do next is run this query, matching the customerID to see what the customers last charge was:
Select serviceID, MAx(dtcreated) as MostRecent
From Transactions
Where (transactiontype = 'Cust Purchase')
Group By serviceID
My Final output combining the two queries would be:
Customerid ServiceID Last Purchase Upgraded?
1 11 11 No
2 21 11 Yes
3 21 12 Yes
4 11 10 Yes
5 12 12 No
6 11 11 No
I thought this might work but it doesn't quite give me what I want. It returns too many results, so the query is obviously not correct.:
Select serviceID, MAx(dtcreated) as MostRecent
From Transactions
WHERE Where (transactiontype = 'Cust Purchase') AND EXISTS
(Select customerid, serviceid
from Transactions
where (dtcreated > #startdate and dtcreated < #enddate) and (transactiontype = 'Cust Save'))
GROUP BY serviceid

Answer 1

If I understand the requirements properly you can use ROW_NUMBER to determine which record is the latest per customerID. Then you can JOIN this back to the transactions table to determine if there is a match in ServiceID:
SELECT r.CustomerID,
t.ServiceID,
t.dtCreated,
Upgraded = CASE WHEN t.ServiceID = cp.ServiceID THEN 0 ELSE 1 END
FROM Transactions AS t
INNER JOIN
( SELECT CustomerID,
ServiceID,
dtCreated,
RowNumber = ROW_NUMBER() OVER(PARTITION BY CustomerID ORDER BY dtCreated DESC)
FROM Transactions
WHERE transactiontype = 'Cust Purchase'
) AS cp
ON cp.CustomerID = t.CustomerID
AND cp.RowNumber = 1
WHERE t.dtcreated > #startdate
AND t.dtcreated < #enddate
AND t.transactiontype = 'Cust Save'

Answer 2

I think you need something like this.
Here t1 gives you the max dtcreated per customer;
t2 contains all transactions in the date range given;
t3 gives you the last purchase per customer.
select
t1.customerid,
t3.serviceid as Last_Purchase_ServiceID,
t1.dtcreated as Last_Purchase_DateCreated,
t2.ServiceID as Current_Purchase_ServiceID,
t2.dtcreated as Current_Purchase_DateCreated
from
(
select customerid, max(dtcreated) as dtcreated
from
Transactions
group by customerid
)
t1
join
(
select customerid, serviceid, dtcreated
from Transactions
where (dtcreated > #startdate and dtcreated < #enddate) and (transactiontype = 'Cust Save')
) t2 on t1.customerid = t2.customerid
join
Transactions t3 on t1.customerid = t3.customerid and t1.dtcreated = t3.dtcreated

Answer 3

Try OUTER APPLY:
Select t.customerid, t.serviceid, o.MostRecent
from Transactions t
OUTER APPLY (
Select MAx(dtcreated) as MostRecent
From Transactions
Where transactiontype = 'Cust Purchase' and Customerid = t.Customerid --And ServiceID = t.ServiceID
) o
where (t.dtcreated > #startdate and t.dtcreated < #enddate) and (t.transactiontype = 'Cust Save')