PERCENT_RANK & DENSE_RANK di Mysql / Posgres

 SELECT

c.customer_id,

o.amount,

PERCENT_RANK() OVER (ORDER BY o.amount) AS percent_rank,

DENSE_RANK() OVER (ORDER BY o.amount DESC) AS dense_rank

FROM orders o

LEFT JOIN customers c

ON c.customer_id = o.customer_id;