MySQL到PostgreSQL：如何修改這個SQL查詢？

Question

我有這樣的MySQL查詢，使得使用的MONTH()和YEAR()：

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) 

我將如何修改查詢PostgreSQL的工作？

Answer 1

 
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) 

在這裏工作是跟上時代的手工
http://www.postgresql.org/docs/current/static/functions-datetime.html#FUNCTIONS-DATETIME-EXTRACT

順便說一句：這是標準（ANSI）SQL，它也適用於MySQL。

Answer 2

http://www.postgresql.org/docs/9.0/static/functions-datetime.html

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(YEAR FROM created_at), EXTRACT(MONTH FROM created_at) 

這句法應該對PostgreSQL的，甲骨文和Teradata