# Why is unit_price used instead of total?

The provided solution uses unit_price instead of using total. The average sales per customer and average order value will vary only if a customer has multiple orders with different invoice_id. If total is used, both of these values are same.

I need help figuring out what is the reason behind the difference in the two results (total, unit_price) and why has unit_price been taken into consideration.

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hi @bhavya
Yes you are right taking sum of `total` make more sense to answer task given in mission, because `total`/sales = `unit_price` * `quantity`
but here in this dataset `quantity` is same for all the tracks in a particular invoice, so, total of `unit_price` of all tracks for particular invoice in `invoice_line` table and `total` in `invoice` is same for any particular invoice.
So whether you take `unit_price` or `total` for calculation you will get the same answer in both the cases when grouping by country, using the `unit_price` is pretty much convenient as far as code is concerned.

Hope this helps!

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HI! @bhavya
If you are satisfied with the answer, it would be great if you could mark it as a solution, so it will help other community members while searching for the same question.

Thank you.
Happy learning!

unit_price and total are not the same as you say. If they were the results would be the same.
I have figured out the solution using total.

``````SELECT
COUNT(DISTINCT(c.customer_id)) total_customers,
COUNT(i.invoice_id) total_orders,
ROUND(SUM(i.total),2) total_sales
FROM invoice i
INNER JOIN customer c ON c.customer_id = i.customer_id
GROUP BY 1;
``````

avg_sales_per_customer = total_sales/total_customers
avg_order_value = total_sales/total_orders

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