Customer Spending vs Country Average

WITH CustomerTotals AS (
    SELECT c.CustomerId,
           c.FirstName || ' ' || c.LastName AS CustomerName,
           c.Country,
           ROUND(SUM(i.Total), 2) AS TotalSpent
    FROM Customer c
    JOIN Invoice i ON c.CustomerId = i.CustomerId
    GROUP BY c.CustomerId
),
CountryAvg AS (
    SELECT Country, ROUND(AVG(TotalSpent), 2) AS AvgSpent
    FROM CustomerTotals
    GROUP BY Country
)
SELECT ct.CustomerName,
       ct.Country,
       ct.TotalSpent,
       ca.AvgSpent AS CountryAvg,
       ROUND(ct.TotalSpent - ca.AvgSpent, 2) AS Difference
FROM CustomerTotals ct
JOIN CountryAvg ca ON ct.Country = ca.Country
WHERE ct.TotalSpent > ca.AvgSpent
ORDER BY Difference DESC
LIMIT 15;