Payment analysis - SQL server query - sql-server

Question

Please can someone give me some pointers.
We are required to send out a Statutory Arrears Notification.
The criteria for sending it out is when an account has missed 2 full payments or the equivalent of. I.e if they are due to pay £100 a month but only paid £50 over 4 months, they are due the notice.
I have pulled a query which separates out the Repayment Schedule into date ranges, and between each range I have tallied up the payments made within that period. Also for each result I have tallied up DueToDate and PaidToDate.
The issue I have is working out some form of scoring system for each row, then at the end of the query, tally up to give an overall score which determines if the notice is due or not.
Results structure is like this.
DueDate | DateFrom | DateTo | AmountDue | AmountPaid | DueToDate | PaidToDate

Answer 1

If you mean that you already have a query that produces a result set like the following
DueDate | DateFrom | DateTo | AmountDue | AmountPaid | DueToDate | PaidToDate
20120301 | 20120201 | 20120229 | 100.00 | 50.00 | 100.00 | 50.00
20120401 | 20120301 | 20120331 | 100.00 | 50.00 | 200.00 | 100.00
20120501 | 20120401 | 20120430 | 100.00 | 50.00 | 300.00 | 150.00
20120601 | 20120501 | 20120531 | 100.00 | 50.00 | 400.00 | 200.00
Then here are two ways forward depending on whether the AmountDue per month is constant. If it is, then you can use
select *
from QueryResult
where DueToDate - PaidToDate >= 2 * AmountPaid;
If it is not constant, then you can use LAG() in SQL Server 2012 to add AmountPaid from the prior row to the current
;WITH Lagged AS (
select *, PriorAmount = LAG(AmountPaid, 1, 0) OVER (order by DueDate)
from QueryResult
)
select *
from Lagged
where DueToDate - PaidToDate >= AmountPaid + PriorAmount;
Or just keep a running total in yet another column in your original query, e.g.
DueDate | DateFrom | DateTo | AmountDue | AmountPaid | DueToDate | PaidToDate | TwoPeriods
20120301 | 20120201 | 20120229 | 100.00 | 50.00 | 100.00 | 50.00 | 100.00
20120401 | 20120301 | 20120331 | 100.00 | 50.00 | 200.00 | 100.00 | 200.00
20120501 | 20120401 | 20120430 | 100.00 | 50.00 | 300.00 | 150.00 | 200.00
20120601 | 20120501 | 20120531 | 100.00 | 50.00 | 400.00 | 200.00 | 200.00