I have the following table in a `MySQL` database:

```
id      whenadded          test1 ..                      test10  avg    std
40  2013-04-16 04:42:27 449 450 450 450 450 450 450 450 451 451 450.1   0.513
44  2013-04-16 07:05:31 460 460 460 461 461 461 461 461 461 462 460.8   0.572
48  2013-04-16 09:05:05 460 461 461 461 461 461 461 462 462 462 461.2   0.572
52  2013-04-16 11:04:11 450 450 450 450 450 450 451 451 451 451 450.4   0.467
56  2013-04-16 13:02:59 449 449 449 450 450 450 450 450 450 450 449.7   0.437

```

which consists of the columns `id`, `whenadded`, `tests 1 to 10`, `avg` and `std`.
I needed to create a `SQL` query that returned me the top `20` latests results, `sorted` by `whenadded (DATETIME)` from the most recent to the 20th recent.
However I was unsure of how to write such a query.
May someone please help me with that?