Have you ever needed to calculate a running total in SQL Server? In this article, we will explore a solution using CROSS JOINS that can help you achieve this without the need for cursors or loops.

Let’s start with a scenario where we have a table called “Accounts” with columns ID, TransactionDate, and Balance. We want to calculate the sum of the last five transactions in an iterative way, resulting in a computed column called “RunningTotal”.

In Excel, we can easily achieve this by using a formula like “SUM(C1:C5)” and copying it to new cells. However, in SQL Server, it is more challenging to add such a computed column that computes data on an iterative level.

Here is a solution using CROSS JOINS:

CREATE TABLE Accounts
(
ID int IDENTITY(1,1),
TransactionDate datetime,
Balance float
)

INSERT INTO Accounts(TransactionDate, Balance) VALUES ('1/1/2000', 100)
INSERT INTO Accounts(TransactionDate, Balance) VALUES ('1/2/2000', 101)
INSERT INTO Accounts(TransactionDate, Balance) VALUES ('1/3/2000', 102)
INSERT INTO Accounts(TransactionDate, Balance) VALUES ('1/4/2000', 103)
INSERT INTO Accounts(TransactionDate, Balance) VALUES ('1/5/2000', 104)
INSERT INTO Accounts(TransactionDate, Balance) VALUES ('1/6/2000', 105)
INSERT INTO Accounts(TransactionDate, Balance) VALUES ('1/7/2000', 106)
INSERT INTO Accounts(TransactionDate, Balance) VALUES ('1/8/2000', 107)
INSERT INTO Accounts(TransactionDate, Balance) VALUES ('1/9/2000', 108)
INSERT INTO Accounts(TransactionDate, Balance) VALUES ('1/10/2000', 109)
INSERT INTO Accounts(TransactionDate, Balance) VALUES ('1/11/2000', 200)
INSERT INTO Accounts(TransactionDate, Balance) VALUES ('1/12/2000', 201)
INSERT INTO Accounts(TransactionDate, Balance) VALUES ('1/13/2000', 202)
INSERT INTO Accounts(TransactionDate, Balance) VALUES ('1/14/2000', 203)
INSERT INTO Accounts(TransactionDate, Balance) VALUES ('1/15/2000', 204)
INSERT INTO Accounts(TransactionDate, Balance) VALUES ('1/16/2000', 205)
INSERT INTO Accounts(TransactionDate, Balance) VALUES ('1/17/2000', 206)
INSERT INTO Accounts(TransactionDate, Balance) VALUES ('1/18/2000', 207)
INSERT INTO Accounts(TransactionDate, Balance) VALUES ('1/19/2000', 208)
INSERT INTO Accounts(TransactionDate, Balance) VALUES ('1/20/2000', 209)

SELECT Acc.ID, CONVERT(varchar(50), TransactionDate, 101) AS TransactionDate, Balance, ISNULL(RunningTotal, '') AS RunningTotal
FROM Accounts Acc
LEFT OUTER JOIN (
    SELECT ID, SUM(Balance) AS RunningTotal
    FROM (
        SELECT A.ID AS ID, B.ID AS BID, B.Balance
        FROM Accounts A
        CROSS JOIN Accounts B
        WHERE B.ID BETWEEN A.ID - 4 AND A.ID AND A.ID > 4
    ) T
    GROUP BY ID
) Bal ON Acc.ID = Bal.ID

By executing the above script, you will get the desired output with the running total calculated after every five transactions.

It is also possible to calculate the running balance on a particular date by adding it to the group by clause.

Using CROSS JOINS can be a more efficient solution compared to using cursors or loops, as it avoids performance degradation. Give it a try and let us know if you have any questions or suggestions in the comments section below.