如何检索按日期分组时的所有ID的最新记录

Question

我需要一个mysql查询，即使记录与日期没有关联，也会根据日期对每个ID采用最新记录。我不确定这是否可能与MySQL，但我感谢您可以给任何帮助。

例如，假设我有如下表：

user_id | total | timestamp 
---------------------------- 
    1 | -15 | jan 1 
    2 | -5 | jan 1 
    3 | -10 | jan 1 
    1 | -4 | jan 2 
    3 | -16 | jan 3 

我想它见下表返回：

user_id | total | timestamp 
---------------------------- 
    1 | -15 | jan 1 
    2 | -5 | jan 1 
    3 | -10 | jan 1 
    1 | -4 | jan 2 
    2 | -5 | jan 2 
    3 | -10 | jan 2 
    1 | -4 | jan 3 
    2 | -5 | jan 3 
    3 | -16 | jan 3 

请让我知道如果你需要进一步澄清。 感谢您的帮助。

Answer 1

SQLFiddle demo

select user_id, 

(select total 
     from t 
     where user_id=t2.user_id 
      and t.timestamp <= t2.timestamp 
order by t.timestamp DESC LIMIT 1) as total, 

timestamp 
from 
(
select user_id,timestamp 
from 
(select distinct user_id from t) t0 
cross join 
(select distinct timestamp from t) t1 
) t2 

order by timestamp,user_id