oracle sql 分组求最大值后，要显示其它列

select

t_a.a,t_a.b,max(t_a.c) c,

?

MAX (t_a.d)KEEP (DENSE_RANK FIRST
????? ORDER BY t_a.c _ DESC)? d_

from t_a

group by

t_a.a,t_a.b

?