MySQL Select grouping and with latest timestamp

Question

I have a table like this:

+----+----+---------------------+---------------+
|lid |uid |timestamp            |token          |
|----+----+---------------------+---------------+
| 10 | 10 | 2014-02-03 12:17:18 | 52efcf118a0ba |
| 45 | 10 | 2014-02-03 12:51:13 | 52efd7046022d |
| 20 | 10 | 2014-02-04 03:47:59 | 52f0a931d3945 |
| 12 | 11 | 2014-02-04 05:21:57 | 52f0bf389371b |
| 34 | 11 | 2014-02-05 06:36:26 | 52f222384fe2d |
| 12 | 11 | 2014-02-05 07:06:42 | 52f229500b403 |
| 32 | 12 | 2014-02-04 05:21:57 | 52f0bf389371b |
| 55 | 12 | 2014-02-05 06:36:26 | 52f222384fe2d |
| 61 | 12 | 2014-02-05 07:06:42 | 52f229500b403 |

lid and uid are foreign keys and the table does not have a unique column.

I want to select rows grouping the uid BUT with the latest timestamp. For example, from the above data i only want these rows:

+----+----+---------------------+---------------+
|lid |uid |timestamp            |token          |
|----+----+---------------------+---------------+
| 20 | 10 | 2014-02-04 03:47:59 | 52f0a931d3945 |
| 12 | 11 | 2014-02-05 07:06:42 | 52f229500b403 |
| 61 | 12 | 2014-02-05 07:06:42 | 52f229500b403 |

Answer 1

Here is a typical way in MySQL:

select t.*
from table t
where not exists (select 1
                  from table t2
                  where t2.uid = t.uid and
                        t2.timestamp > t.timestamp
                 );

The logic is: get me all rows from the table, where there is no timestamp for the same uid larger than this timestamp. You should have an index on table(uid, timestamp) for performance.