sum() over로 해봤습니다~

with t as (
select 'AAA' code from dual union all
select 'AAA' code from dual union all
select 'AAA' code from dual union all
select 'AAA' code from dual union all
select 'BBB' code from dual union all
select 'BBB' code from dual union all
select 'AAA' code from dual union all
select 'AAA' code from dual union all
select 'BBB' code from dual
)
select code, sum(flag) over(order by rn)
from (
select code, rn, decode(lag(code) over(order by rn), code, 0, 1) flag
from (select code, rownum rn from t)
)

-- 정렬 기준항목이 필요한 문제입니다.
WITH t AS
(
SELECT 1 seq, 'AAA' dept FROM dual
UNION ALL SELECT 2, 'AAA' FROM dual
UNION ALL SELECT 3, 'AAA' FROM dual
UNION ALL SELECT 4, 'AAA' FROM dual
UNION ALL SELECT 5, 'BBB' FROM dual
UNION ALL SELECT 6, 'BBB' FROM dual
UNION ALL SELECT 7, 'AAA' FROM dual
UNION ALL SELECT 8, 'AAA' FROM dual
UNION ALL SELECT 9, 'BBB' FROM dual
)
SELECT seq
     , dept
     , SUM(flag) OVER(ORDER BY seq) grp
  FROM (SELECT seq
             , dept
             , DECODE(LAG(dept) OVER(ORDER BY seq), dept, 0, 1) flag
          FROM t
        )
;