Question

I have the following table with messages:

+---------+---------+------------+----------+
| msg_id  | user_id | _date      | _time    |
+-------------------+------------+----------+
|   1     | 1       | 2011-01-22 | 06:23:11 |
|   2     | 1       | 2011-01-23 | 16:17:03 |
|   3     | 1       | 2011-01-23 | 17:05:45 |
|   4     | 2       | 2011-01-22 | 23:58:13 |
|   5     | 2       | 2011-01-23 | 23:59:32 |
|   6     | 3       | 2011-01-22 | 13:45:00 |
|   7     | 3       | 2011-01-23 | 13:22:34 |
|   8     | 3       | 2011-01-23 | 18:22:34 |
+---------+---------+------------+----------+

What I want is for each day, to see how many messages each user has sent BEFORE and AFTER 16:00. I now do this in two steps:

SELECT user_id, _date, COUNT(msg_id) AS cnt 
FROM messages WHERE _time <= '16:00'
GROUP BY user_id, _date ORDER BY user_id, _date ASC

user_id _date       cnt
-----------------------------
1       2011-01-22  1
1       2011-01-23  0
2       2011-01-22  0
2       2011-01-23  0
3       2011-01-22  1
3       2011-01-23  1

SELECT user_id, _date, COUNT(msg_id) AS cnt 
FROM messages WHERE _time > '16:00'
GROUP BY user_id, _date ORDER BY user_id, _date ASC

user_id _date       cnt
-----------------------------
1       2011-01-22  0
1       2011-01-23  2
2       2011-01-22  1
2       2011-01-23  1
3       2011-01-22  0
3       2011-01-23  1

(In reality, btw, the rows with “0” value aren’t given in the resultset. I just added them for clarification)

I would like to combine these two outputs into one:

user_id _date       before16  after16
-------------------------------------
1       2011-01-22  1         0
1       2011-01-23  0         2
2       2011-01-22  0         1
2       2011-01-23  0         1
3       2011-01-22  1         0
3       2011-01-23  1         1

However, I have no idea on how to write this query. If you do, your help would be appreciated 🙂

Answer 1

Try this:

SELECT 
    user_id, 
    _date, 
    SUM(_time <= '16:00') AS before16, 
    SUM(_time > '16:00') AS after16 
FROM messages 
GROUP BY user_id, _date
ORDER BY user_id, _date ASC