Deserts of Silence :Find the Longest Gaps Between Customer Orders to Identify Periods of Inactivity Intermediate

          with ordered as
  (select customerid,
          orderdate::date as order_date,
          LAG(orderdate::date) over (partition by customerid
                                     order by orderdate) as prev_order_date
   from orders),
     gaps as
  (select customerid,
          (order_date - prev_order_date) as gap_days
   from ordered
   where prev_order_date is not null)
select customerid,
       MAX(gap_days) as longest_gap_days
from gaps
group by customerid
order by longest_gap_days desc,
         customerid;