MySQL的一个分组需求

system1，system2，system3，version，num
1,2,3，v1,2
1,2,3，v2,3
1,2,3，v3,4
1,2,4，v1,2
1,2,4，v2,5

create table t_version(c1 int,c2 int,c3 int,c4 varchar(10),c5 int);

(select c1, c5 from t_version where c1 = (select max(c1) from t_version) limit 1)
union all
(select c2, c5 from t_version where c2 = (select max(c2) from t_version) limit 1)
union all
(select c3, c5 from t_version where c3 = (select max(c3) from t_version) limit 1)

select * from t_version
where (c1, c2, c3, c4) 
in (select c1, c2, c3, max(c4)  
from t_version
group by c1, c2, c3);