Use NTILE(4) to Divide Customers into Revenue Quartiles
Customers Table:

Payments Table:

Query Explanation:
The inner query calculates TotalRevenue per customer by summing their payments.
The outer query uses NTILE(4) to assign each customer to one of four quartiles:
Quartile 1: Highest spenders
Quartile 4: Lowest spenders
ORDER BY TotalRevenue DESC: ensures that higher revenue customers fall into the first quartile.
SQL Query:
SELECT
CustomerID,
TotalRevenue,
NTILE(4) OVER (ORDER BY TotalRevenue DESC) AS RevenueQuartile
FROM (
SELECT
CustomerID,
SUM(Amount) AS TotalRevenue
FROM
Payments
GROUP BY
CustomerID
) AS CustomerRevenue;
Output:

