SQL查询，用于获取一个月中的每个第一个事件（按日期时间字段）

Question

I have table like events ( id , date , event_name , user_id ) and records like

(1, '2013-12-01 08:30:00', 'login', 9),
(2, '2013-12-01 08:33:00', 'login', 4),
(3, '2013-12-01 10:22:00', 'logout', 9),
(4, '2013-12-02 08:34:00', 'login', 9),
...

I need to fetch every first event for each (or specified) user in a day for every days in a month. for ex:

2013-12-01 08:30:00, login, 9
2013-12-02 08:34:00, login, 0
...

Help me to construct properly SQL query

Answer 1

SELECT events.*
FROM
  events INNER JOIN (SELECT user_id,
                            DATE(`date`) as day_event,
                            MIN(`date`) AS first_event
                     FROM   events
                     GROUP BY
                            user_id,
                            DATE(`date`)) fe
  ON events.user_id = fe.user_id
     AND events.`date` = fe.first_event

Please see fiddle here .

If you only want to return a month, you can put your condition in your subquery:

(SELECT user_id,
        DATE(`date`) as day_event,
        MIN(`date`) AS first_event
 FROM   events
 WHERE  `date` >= '2013-12-01' AND `date` < '2014-01-01'
 GROUP BY
        user_id,
        DATE(`date`)) fe

Answer 2

Try this---

SELECT * 
FROM events 
WHERE id IN (SELECT min(id) 
             FROM events 
             GROUP BY user_id, date)