with pl as (
  select
    *,
    row_number() over (partition by session_id order by ex_timestamp) r
  from PROCESS_LOG
),
valid_sessions as (
    select
      *
    from pl p1
    where
      p1.process_id = "STEP" || r
      and
      not exists ( 
        select 1 from pl p2 
        where
          p1.session_id = p2.session_id and
          p1.ex_timestamp > p2.ex_timestamp and
          p2.process_id <> "STEP" || r
      )
)
select 
  process_id PROCESS,
  count(0) CNT
from valid_sessions
group by process_id
order by process_id