Date distinct count over week

You can use window functions and aggregation:

select date, iso_week, sum(case when rn = 1 then 1 else 0 end) cnt
from (
    select t.*, 
        row_number() over(partition by userid, iso_week order by date) min_date
    from mytable t
) t
group by date, iso_week

Better yet, using the standard where clause to aggregate functions, which Presto supports:

select date, iso_week, count(*) filter(where rn = 1) cnt
from (
    select t.*, 
        row_number() over(partition by userid, iso_week order by date) min_date
    from mytable t
) t
group by date, iso_week