Select the First Row In Each Group of MySQL
Here is an example:
SELECT
MIN(purchases2.id), # change to MAX if you want the highest value
purchases1.customer,
purchases1.total
FROM
PURCHASES purchases1
JOIN (SELECT p.customer,
MAX(total) AS max_total
FROM PURCHASES purchases
GROUP BY p.customer) purchases2
ON purchases2.customer = purchases1.customer
AND purchases2.max_total = purchases1.total
GROUP BY purchases1.customer, purchases1.total