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-DA TETIME-EXTRACT

Btw：这也是在MySQL上也可以使用的标准（ANSI）SQL。

Btw: This is standard (ANSI) SQL that works on MySQL as well.