Orders above the customer's own average

A fraud analyst wants to spot orders that are unusually large for that particular customer, not compared with the whole platform.

From customer_orders, return order_id, customer_id, order_amount and customer_avg (that customer's average order amount, rounded to 2 decimals) for every order strictly above the customer's own average. Order by customer_id, then order_id.

1. Step 1: The inner query is a correlated subquery: it references `o.customer_id` from the outer query, so it is re-evaluated for each customer.
2. Step 2: The comparison is strict (`>`), so customer 105, whose two orders both equal the average, returns nothing.
3. Step 3: The same subquery is used once in `SELECT` to display the average and once in `WHERE` to filter.

SELECT o.order_id,
       o.customer_id,
       o.order_amount,
       (SELECT ROUND(AVG(i.order_amount), 2)
          FROM customer_orders i
         WHERE i.customer_id = o.customer_id) AS customer_avg
FROM customer_orders o
WHERE o.order_amount > (SELECT AVG(i.order_amount)
                          FROM customer_orders i
                         WHERE i.customer_id = o.customer_id)
ORDER BY o.customer_id, o.order_id;