create table test_002 (col_1 number, col_2 number);

insert into test_002 values (1,4);
insert into test_002 values (2,5);
insert into test_002 values (4,6);
insert into test_002 values (6,7);
insert into test_002 values (8,8);

select col_1,col_2
from  (select col_1
             ,col_2
             , max(case when col_2 =6 then col_1 else null end) over () x
       from   test_002)
where col_1 >= x;

     COL_1      COL_2
---------- ----------
         4          6
         6          7
         8          8