with t (a,rn) as (
   select 'AAA', 1 from dual union all
   select 'AAA', 2 from dual union all
   select 'AAA', 3 from dual union all
   select 'BBB', 4 from dual union all
   select 'BBB', 5 from dual union all
   select 'AAA', 6 from dual union all
   select 'AAA', 7 from dual 
)
select rn, a, classifier, match_number
from t
match_recognize(
     order by RN
     measures
        CLASSIFIER() AS CLASSIFIER,
        MATCH_NUMBER() AS MATCH_NUMBER
     all rows per match
     pattern (strt next*)
         define next as next.a = prev(a)
)
/
        RN A   CLASSIFIER MATCH_NUMBER
---------- --- ---------- ------------
         1 AAA STRT                  1
         2 AAA NEXT                  1
         3 AAA NEXT                  1
         4 BBB STRT                  2
         5 BBB NEXT                  2
         6 AAA STRT                  3
         7 AAA NEXT                  3