SELECT * FROM customers WHERE id IN (SELECT customer_id FROM orders GROUP BY customer_id HAVING SUM(total) > (SELECT AVG(total_spend) FROM (SELECT SUM(total) AS total_spend FROM orders GROUP BY customer_id) t));

WITH customer_totals AS (
  SELECT customer_id, SUM(total) AS total_spend
  FROM orders GROUP BY customer_id
),
avg_spend AS (
  SELECT AVG(total_spend) AS avg_total FROM customer_totals
)
SELECT c.* FROM customers c
JOIN customer_totals ct ON c.id = ct.customer_id
WHERE ct.total_spend > (SELECT avg_total FROM avg_spend);

SELECT * FROM customers c WHERE (SELECT SUM(total) FROM orders WHERE customer_id = c.id) > (SELECT AVG(total) FROM orders);

SELECT customer_id FROM orders GROUP BY customer_id HAVING SUM(total) > AVG(total);