轉換mysql到postgresql

Question

我有一個工作的MySQL查詢，但我不能讓它與postgres一起工作。這是查詢（我已經改變日期格式TO_CHAR

SELECT country as grouper, date(users.created_at) as date, 
     to_char(users.created_at, '%Y-%m') as date_group, 
     count(id) as total_count 
    FROM "users" 
WHERE (users.created_at >= '2011-12-01') 
    AND (users.created_at <= '2014-02-11') 
GROUP BY grouper, date_group 
ORDER BY date ASC 

我得到的錯誤：

PG::Error: ERROR: column "users.created_at" must appear in the GROUP BY clause or be used in an aggregate function 
LINE 1: SELECT country as grouper, date(users.created_at) as date, t... 

感謝您的幫助

Answer 1

SELECT country as grouper, date(MIN(users.created_at)) as date, 
     to_char(MIN(users.created_at), '%Y-%m') as date_group, 
     count(id) as total_count 
    FROM "users" 
HAVING (users.created_at >= '2011-12-01') 
    AND (users.created_at <= '2014-02-11') 
GROUP BY grouper, date_group 
ORDER BY date ASC 

MySQL不是很嚴格。在符合標準的SQL中，所有列值必須在非分組字段上使用聚合函數（SUM，COUNT，MAX，MIN） - 使用GROUP BY時。

老實說，我不完全確定GROUP BY中的data_group;它可以被丟棄嗎？ 另外請注意，我已經與HAVING切換。

Answer 2

你應該在集團利用每一個選定列BY節。

SELECT country as grouper, to_char(created_at, '%Y-%u') as date_group, count(id) as total_count 
FROM "users" 
WHERE created_at >= '2013-10-01' 
AND created_at <= '2014-02-11' 
GROUP BY grouper, date_group 
ORDER BY date_group ASC