with a as (
    select
        session_id,
        process_id,
        rank() over(
            partition by session_id
            order by
                EX_TIMESTAMP
        ) rnk
    from
        PROCESS_LOG
)
select
    process_id as PROCESS,
    count(*) as CNT
from
    (
        select
            x.session_id,
            x.process_id 
        from
            a x
            left join (
                select
                    *
                from
                    a
                where
                    process_id = 'STEP' || rnk
            ) y on x.session_id = y.session_id
            and x.process_id >= y.process_id
        group by
            x.session_id,
            x.process_id
        having
            count(y.session_id) == x.rnk

) tbl
group by
    process_id
order by
    process_id;