I found a faster solution (at least on this small dataset).

;

WITH totals AS (

SELECT *, ABS(Amount) AS Amt, SUM(ABS(Amount)) OVER(PARTITION BY Customer, TransactionType ORDER BY Date ROWS UNBOUNDED PRECEDING ) AS tot

FROM #t1

)

, balances AS (

SELECT *, MIN(CASE WHEN TransactionType = 'Debit' THEN Date END) OVER(PARTITION BY Customer ORDER BY tot, TransactionType ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING) AS PaidDate,

LAG(TransactionType) OVER(PARTITION BY Customer ORDER BY tot, TransactionType) AS PrevTransactionType,

LAG(Date) OVER(PARTITION BY Customer ORDER BY tot, TransactionType) AS PrevDate,

LAG(tot) OVER(PARTITION BY Customer ORDER BY tot, TransactionType) AS PrevTot

FROM totals

)

SELECT TransactionID, Customer,

CASE

WHEN PaidDate IS NOT NULL THEN 0

WHEN PrevTransactionType = 'Credit' THEN Amt

ELSE tot - PrevTot

END AS RemainingBalance,

CASE

WHEN PaidDate IS NOT NULL THEN PaidDate

WHEN PrevTransactionType = 'Debit' THEN PrevDate

END AS LastRedeemedDate

FROM balances

WHERE TransactionType = 'Credit'

ORDER BY tot, TransactionType

If I have the time, I'll run a more complete set.

Drew