I am trying to create a cumulative total for the Paid column (SUMPaid),
grouped by Contract and Ordered by Year.

I tried using SUM with Partition By but that SUMs the group from the first line,
I tried using LAG + LAG(Paid,1) but that sums only the previous column which wont
work when there are 3 years in the contract (200662)

[Paid] + LAG([Paid],1) OVER (PARTITION BY Contract ORDER BY [Year])

Can anyone suggest how to do this ?