MySQL Group By with top N number of each kind

Question

I have a table like this:

Rank      Letter
1         A
2         A
3         B
4         A
5         C
6         A
7         C
8         C
9         B
10        C 

And I need the top 2 of each letter ordered by ascending rank:

Rank      Letter
1         A
2         A
3         B
5         C
7         C
9         B

How would I do it? It's fairly straightforward to get just the top 1 using GROUP BY, but I can't seem to get it working for multiple entries

Answer 1

select distinct rank, letter
  from table1 t2
 where rank in 
         (select top 2 rank
            from table1 t2 
           where t2.letter = t1.letter 
           order by rank)
       order by letter, rank

EDIT: (my first try won't work on MySql (Quassnoi comment), I modified it to work on sql server for example)

second try:

select t.letter, t.rank
from table1 t
join (
    select t1.letter, min(t1.rank) m
    from table1 t1
    join (select t0.letter, min(t0.rank) m, count(1) c 
           from table1 t0 group by t0.letter) t2
    on t1.letter = t2.letter and ((t2.c = 1) or (t2.c > 1 and t1.rank > m))
    group by t1.letter) t3 
  on t.letter = t3.letter and t.rank <= t3.m