select s_date from tablename where b in (select max(b) from tablename group by s_found)
这样就可以了，用了group by 前面就要用函数而不是某个字段。
SELECT s_fund,max(b) as maxb FROM test1
GROUP BY s_fund
看下此图；符合你说的 获取s_fund=aaa和s_fund=bbb中的b最大的那一行；
select * from (
select *,row_number() over(partition by s_fund order by b desc ) rn from tablename )
where rn = 1
