query help

I know its probably a simple query, but I've spent a long time on it and could not figure it out.

I'm trying to select distinct fieldA in the table, such that fieldB is smallest within each fieldA. Suppose the table has following rows:

P_Key fieldA fieldB

1     1      5
2     1      4
3     2      4
4     2      3

The result of the query would look like:

P_Key fieldA fieldB

2     1      4
4     2      3