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
编辑：（我的第一次尝试将无法在MySql（Quassnoi注释）上工作，例如，我将其修改为可在sql服务器上工作）
第二次尝试：
select t.letter, t.rankfrom table1 tjoin ( 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
