T-SQL Grouping with LESS THAN {date} that breaks off on each occurrence of date - tsql

Question

I am struggling with creating a grouping using LESS THAN that breaks off on each date for the parent row. I have created a contrived example to explain the data and what I would like out as a result:
CREATE TABLE [dbo].[CustomerOrderPoints](
[CustomerID] [int] NOT NULL,
[OrderPoints] [int] NOT NULL,
[OrderPointsExpiry] [date] NOT NULL
) ON [PRIMARY]
GO
CREATE TABLE [dbo].[CustomerOrderPointsUsed](
[CustomerID] [int] NOT NULL,
[OrderPointsUsed] [int] NOT NULL,
[OrderPointsUseDate] [date] NOT NULL
) ON [PRIMARY]
GO
INSERT [dbo].[CustomerOrderPoints] ([CustomerID], [OrderPoints], [OrderPointsExpiry]) VALUES (10, 200, CAST(N'2018-03-18' AS Date))
GO
INSERT [dbo].[CustomerOrderPoints] ([CustomerID], [OrderPoints], [OrderPointsExpiry]) VALUES (10, 100, CAST(N'2018-04-18' AS Date))
GO
INSERT [dbo].[CustomerOrderPoints] ([CustomerID], [OrderPoints], [OrderPointsExpiry]) VALUES (20, 120, CAST(N'2018-05-10' AS Date))
GO
INSERT [dbo].[CustomerOrderPoints] ([CustomerID], [OrderPoints], [OrderPointsExpiry]) VALUES (30, 75, CAST(N'2018-02-10' AS Date))
GO
INSERT [dbo].[CustomerOrderPoints] ([CustomerID], [OrderPoints], [OrderPointsExpiry]) VALUES (30, 60, CAST(N'2018-04-24' AS Date))
GO
INSERT [dbo].[CustomerOrderPoints] ([CustomerID], [OrderPoints], [OrderPointsExpiry]) VALUES (30, 90, CAST(N'2018-06-25' AS Date))
GO
INSERT [dbo].[CustomerOrderPoints] ([CustomerID], [OrderPoints], [OrderPointsExpiry]) VALUES (40, 100, CAST(N'2018-06-13' AS Date))
GO
INSERT [dbo].[CustomerOrderPointsUsed] ([CustomerID], [OrderPointsUsed], [OrderPointsUseDate]) VALUES (10, 15, CAST(N'2018-02-10' AS Date))
GO
INSERT [dbo].[CustomerOrderPointsUsed] ([CustomerID], [OrderPointsUsed], [OrderPointsUseDate]) VALUES (10, 30, CAST(N'2018-02-17' AS Date))
GO
INSERT [dbo].[CustomerOrderPointsUsed] ([CustomerID], [OrderPointsUsed], [OrderPointsUseDate]) VALUES (10, 25, CAST(N'2018-03-16' AS Date))
GO
INSERT [dbo].[CustomerOrderPointsUsed] ([CustomerID], [OrderPointsUsed], [OrderPointsUseDate]) VALUES (10, 45, CAST(N'2018-04-10' AS Date))
GO
INSERT [dbo].[CustomerOrderPointsUsed] ([CustomerID], [OrderPointsUsed], [OrderPointsUseDate]) VALUES (20, 10, CAST(N'2018-02-08' AS Date))
GO
INSERT [dbo].[CustomerOrderPointsUsed] ([CustomerID], [OrderPointsUsed], [OrderPointsUseDate]) VALUES (20, 70, CAST(N'2018-04-29' AS Date))
GO
INSERT [dbo].[CustomerOrderPointsUsed] ([CustomerID], [OrderPointsUsed], [OrderPointsUseDate]) VALUES (20, 25, CAST(N'2018-05-29' AS Date))
GO
INSERT [dbo].[CustomerOrderPointsUsed] ([CustomerID], [OrderPointsUsed], [OrderPointsUseDate]) VALUES (30, 60, CAST(N'2018-02-05' AS Date))
GO
INSERT [dbo].[CustomerOrderPointsUsed] ([CustomerID], [OrderPointsUsed], [OrderPointsUseDate]) VALUES (30, 30, CAST(N'2018-03-13' AS Date))
GO
INSERT [dbo].[CustomerOrderPointsUsed] ([CustomerID], [OrderPointsUsed], [OrderPointsUseDate]) VALUES (40, 120, CAST(N'2018-06-10' AS Date))
Customers gain points, which have an expiry. We have a CustomerOrderPoints table which shows OrderPoints for customers together with the Expiry date for the points. A Customer may have many rows in this table.
We then also have the CustomerOrderPointsUsed table which shows the points that have been used and when they were used by a Customer.
I am trying to get a grouping of Customer data which will show OrderPoints used as a group against each customer but, separated on the ExpiryDate. The picture below shows an example of the Grouped Results that I would like to obtain.
We have bad, but working code that has been developed using a recursive method (RBAR), but it is very slow. I have tried a number of different SET Based grouping approaches, but cannot get the final Less Than grouping which takes into account the previous expiry dates.
This DB is on SQL Server 2008R2. Ideally I am looking for a solution that will work with SQL Server 2008R2, but will welcome options for later versions, as we may need to move this particular DB to solve this problem.
I have tried using a combination of RanK, DenseRank and RowNumber (for later versions) and LAG, but have not been able to get anything working that can be built upon.
Is there a way to use SET based T-SQL to achieve this?

Answer 1

First - this is ignoring the question I raised in the comments above, and just allocates all rows to the expiry date on or after the use by date. You would need to rethink this if you need to split one use among multiple expiry dates
First, allocate an expiry date to each PointsUsed row. This is done by joining to all OrderPoints rows with an expiry date on or after the UseDate, then taking the minimum date.
Then the second query reports all OrderPoints rows, joining to the first query by the allocated expiry date, which has all the data needed.
WITH allocatedPoints as
(
Select U.CustomerID, U.OrderPointsUsed, MIN(P.OrderPointsExpiry) as OrderPointsExpiry
from CustomerOrderPointsUsed U
inner join CustomerOrderPoints P on P.CustomerID = U.CustomerID and P.OrderPointsExpiry >= U.OrderPointsUseDate
GROUP BY U.CustomerID, U.OrderPointsUseDate, U.OrderPointsUsed
)
Select P.CustomerID, P.OrderPoints, P.OrderPointsExpiry,
ISNULL(SUM(AP.OrderPointsUsed), 0) as used,
P.OrderPoints - ISNULL(SUM(AP.OrderPointsUsed), 0) as remaining
from CustomerOrderPoints P
left outer join allocatedPoints AP on AP.CustomerID = P.CustomerID and AP.OrderPointsExpiry = P.OrderPointsExpiry
GROUP BY P.CustomerID, P.OrderPoints, P.OrderPointsExpiry