Select row with most recent date per user

I have a table (“lms_attendance”) of users’ check-in and out times that looks like this:

id  user    time    io (enum)
1   9   1370931202  out
2   9   1370931664  out
3   6   1370932128  out
4   12  1370932128  out
5   12  1370933037  in

I’m trying to create a view of this table that would output only the most recent record per user id, while giving me the “in” or “out” value, so something like:

id  user    time    io
2   9   1370931664  out
3   6   1370932128  out
5   12  1370933037  in

I’m pretty close so far, but I realized that views won’t accept subquerys, which is making it a lot harder. The closest query I got was :

select 
    `lms_attendance`.`id` AS `id`,
    `lms_attendance`.`user` AS `user`,
    max(`lms_attendance`.`time`) AS `time`,
    `lms_attendance`.`io` AS `io` 
from `lms_attendance` 
group by 
    `lms_attendance`.`user`, 
    `lms_attendance`.`io`

But what I get is :

id  user    time    io
3   6   1370932128  out
1   9   1370931664  out
5   12  1370933037  in
4   12  1370932128  out

Which is close, but not perfect. I know that last group by shouldn’t be there, but without it, it returns the most recent time, but not with it’s relative IO value.

Any ideas? Thanks!

Answer

Query:

SQLFIDDLEExample

SELECT t1.*
FROM lms_attendance t1
WHERE t1.time = (SELECT MAX(t2.time)
                 FROM lms_attendance t2
                 WHERE t2.user = t1.user)

Result:

| ID | USER |       TIME |  IO |
--------------------------------
|  2 |    9 | 1370931664 | out |
|  3 |    6 | 1370932128 | out |
|  5 |   12 | 1370933037 |  in |

Note that if a user has multiple records with the same “maximum” time, the query above will return more than one record. If you only want 1 record per user, use the query below:

SQLFIDDLEExample

SELECT t1.*
FROM lms_attendance t1
WHERE t1.id = (SELECT t2.id
                 FROM lms_attendance t2
                 WHERE t2.user = t1.user            
                 ORDER BY t2.id DESC
                 LIMIT 1)