MySQL到PostgreSQL：如何修改这个SQL查询？

我有这个使用MONTH()和YEAR()的MySQL查询：

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

如何修改该查询以使用Postgresql？

解决方法:

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) 

这是最新的手册
http://www.postgresql.org/docs/current/static/functions-datetime.html#FUNCTIONS-DATETIME-EXTRACT

顺便说一句：这是适用于MysqL的标准(ANSI)sql.