Atualizando coluna com base no registro anterior

select t.*,
       (row_number() over (partition by c1, c2, c3, c4, c5 order by c6) - 1
       ) as "Count"
from t;

update t
    set count = (select count(*)
                 from t t2
                 where t2.col1 = t.col1 and t2.col2 = t.col2 and t2.col3 = t.col3 and
                       t2.col4 = t.col4 and t.col5 = t2.col5 and
                       t2.col6 < t.col6
                );