with tb_test as (

select '1' as seq, 'A' as status, null as pre_seq from dual

union select '2' as seq, 'A' as status, '3' as pre_seq from dual

union select '3' as seq, 'B' as status, null as pre_seq from dual

union select '4' as seq, 'A' as status, '5' as pre_seq from dual

union select '5' as seq, 'B' as status, null as pre_seq from dual

union select '6' as seq, 'A' as status, '7' as pre_seq from dual

union select '7' as seq, 'C' as status, null as pre_seq from dual

) select * from tb_test

seq 1은 정상적으로 처리된 상태,

seq 2는  seq 3에 의해서 취소된 상태 (seq 2의 pre_seq가 3이고 3의 status 가 'B'),

seq 4는 seq 5에 의해서 취소된 상태 (seq 4의 pre_seq가 5이고 5의 status 가 'B'),

seq 6은 seq 7을 하는데 사용된 상태라고 할때 (seq 6의 pre_seq가 7이고 7의 status 가 'C')

seq1과 seq6의 count를 구하고 싶습니다.

어떻게 하면 될까요..?? 하루종일 이리저리 해봤는데.. 답이 안나오네요..