jak uzyskać pozycję posortowanych wierszy za pomocą mysql i php

Można to zrobić na dwa sposoby:

Metoda 1:

SET @i = 0;

SELECT * FROM 
scores s1 INNER JOIN (SELECT *, @i := @i + 1 AS rank FROM scores ORDER BY score DESC) AS s2 USING (id);

Metoda 2:

SELECT *, (SELECT COUNT(1) AS num FROM scores WHERE scores.score > s1.score) + 1 AS rank FROM scores AS s1
ORDER BY rank asc