with substract as (
with ac_c as(
    select t.id, t.dt, t.ac
    from table_1 t
    where t.ac is not NULL
),
co_c as(
    select t.id, t.dt, t.co
    from table_1 t
    where t.co is not NULL
)
select (date(co_c.dt)-date(ac_c.dt)) as subs
from ac_c, co_c
where ac_c.id = co_c.id
)

select subs, count(*)
from substract
group by subs