MySQL vers PostgreSQL :Comment modifier cette requête SQL ?

SELECT 
  extract(MONTH from created_at) AS month, 
  extract(YEAR from created_at) AS year 
FROM users 
GROUP BY extract(MONTH from created_at), extract(YEAR from created_at) 
ORDER BY extract(MONTH from created_at), extract(YEAR from created_at) 

Voici le manuel à jour
http://www.postgresql.org/docs/current/static/functions-datetime.html#FUNCTIONS-DATETIME-EXTRACT

Au fait :il s'agit d'un SQL standard (ANSI) qui fonctionne également sur MySQL.