select tb.* from
(select a,c cc,max(d) dd from
(select tb.* from
(select a,max(c) cc from tb
group by a
) tba
left join tb on tb.a=tba.a and tb.c=tba.cc
) tba
group by a,c
) tba
left join tb on tb.a=tba.a and tb.c=tba.cc and tb.d=tba.dd