Calculate running total / running balance

Question

I have a table:

create table Transactions(Tid int,amt int)

With 5 rows:

insert into Transactions values(1, 100)
insert into         


        

Answer 1

We're on 2008R2 and I use variables and a temp table. This also allows you to do custom things when calculating each row using a case statement (i.e. certain transactions may act differently, or you may only want a total for specific transaction types)

DECLARE @RunningBalance int = 0
SELECT Tid, Amt, 0 AS RunningBalance
INTO #TxnTable
FROM Transactions
ORDER BY Tid

UPDATE #TxnTable
SET @RunningBalance = RunningBalance = @RunningBalance + Amt

SELECT * FROM #TxnTable
DROP TABLE #TxnTable

We have a transaction table with 2.3 million rows with an item that has over 3,300 transactions, and running this type of query against that takes no time at all.