How do I show a running total from the previous records?

Question

I wonder if someone can please assist.

I have the following code which basically inserts 10 records into a table. From this table I'm trying to show a running total for the amount of sales against the seller. I've tried using the LAG function but that does not appear to work.

Here is the code.

CREATE TABLE Sales 
(
    OrderId Int NOT NULL,
    Seller  varchar(10) NULL,
    Amount  money NULL
)

INSERT INTO Sales VALUES
    (1, 'Alex', 10.00),
    (2, 'Sarah', 15.00),
    (3, 'Tracy', 10.25),
    (4, 'Pete', 10.25),
    (5, 'Tracy', 11.00),
    (6, 'Tracy', 10.25),
    (7, 'Alex', 10.25),
    (8, 'Jane', 10.25),
    (9, 'Alex', 20.55)

SELECT Seller, Amount, LAG(Amount,1) OVER (PARTITION BY Seller ORDER BY Seller) AS RunningTotal FROM Sales

Essentially in this example I would expect the following output

Seller|Amount|Running Total
Alex|10.00|10.00
Alex|1.25|20.25
Alex|20.55|40.90
Jane|10.25|10.25
Pete|10.25|10.25
Sarah|15.00|15.00
Tracy|10.25|10.25
Tracy|11.00|21.25
Tracy|10.25|31.50

Hope someone can help and thanks in advance. Dave

Answer 1

I am guessing you have an sql server, but it should alspo work on other rdms that support window functions

SELECT 
Seller
, Amount
, SUM(Amount) OVER (PARTITION BY Seller ORDER BY Seller ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) AS RunningTotal 
FROM Sales
GO

Seller |  Amount | RunningTotal
:----- | ------: | -----------:
Alex   | 10.0000 |      10.0000
Alex   | 10.2500 |      20.2500
Alex   | 20.5500 |      40.8000
Jane   | 10.2500 |      10.2500
Pete   | 10.2500 |      10.2500
Sarah  | 15.0000 |      15.0000
Tracy  | 10.2500 |      10.2500
Tracy  | 11.0000 |      21.2500
Tracy  | 10.2500 |      31.5000

db<>fiddle here