LAG로 비교하면 어떨까요

with t (item, dt, lv) as (
select 'A', '1일', '1등급' from dual union all
select 'A', '2일', '1등급' from dual union all
select 'A', '3일', '1등급' from dual union all
select 'A', '4일', '2등급' from dual union all
select 'A', '5일', '2등급' from dual union all
select 'A', '6일', '1등급' from dual union all
select 'A', '7일', '1등급' from dual union all
select 'A', '8일', '1등급' from dual union all
select 'A', '9일', '3등급' from dual
)
select dt, lv
from (
select item, dt, lv, lag(lv,1,0) over (order by dt) lag from t
)
where lv <> lag