Faça isso na hora da consulta:
with t (year, folder, seq_no) as (values
(1973,5,11),
(2010,4,7),
(1973,11,12),
(1973,5,11),
(1500,4,4),
(2010,4,7)
)
select
dense_rank() over (order by year, folder, seq_no) as id,
year, folder, seq_no,
count(*) over (partition by year, folder, seq_no) as "count"
from t
;
id | year | folder | seq_no | count
----+------+--------+--------+-------
1 | 1500 | 4 | 4 | 1
2 | 1973 | 5 | 11 | 2
2 | 1973 | 5 | 11 | 2
3 | 1973 | 11 | 12 | 1
4 | 2010 | 4 | 7 | 2
4 | 2010 | 4 | 7 | 2
