# Running Total; 7. Joining on Conditions (Continuation)

The Instructions are to Write a query that displays one invoice per row with the following data:

The invoice ID
The date of the invoice
The total of the invoice
The running total for the invoice, rounded to two decimal places aliased as running_total

When I run the below code, I beleive I get the asnwer required for the excercise however it’s not being accepted… what is the reason this is incorrect?

``````  SELECT i1.invoice_id, i1.invoice_date, i1.total, ROUND(SUM(i2.total), 2) AS running_total
FROM invoice i1
JOIN invoice i2
ON i1.invoice_id >= i2.invoice_id AND i1.invoice_date >= i2.invoice_date
GROUP BY i1.invoice_id;
``````

I’m not getting the understanding from the lessons THE WHY that provides logic for certain information belonging with particular caluses.
As far as I understand, I have grouped the invoice row to meet the requirement to display one invoice per row.

``````Your GROUP BY clause is using less expressions than expected. It should have 3 expressions in total but only has 1.
``````

I’ve found that the correct answer is
SELECT i1.invoice_id, i1.invoice_date, i1.total, ROUND(SUM(i2.total), 2) AS running_total
FROM invoice i1
JOIN invoice i2
ON i1.invoice_id >= i2.invoice_id AND i1.invoice_date >= i2.invoice_date
GROUP BY i1.invoice_id, i1.invoice_date, i1.total;