with tmp0 as (
    select
        session_id,
        process_id,
        lag(process_id, 1) over (
            partition by session_id
            order by ex_timestamp asc
        ) as prev_process_id,
        ex_timestamp
    from process_log
),
tmp1 as (
    select
        session_id,
        process_id,
        case
            when process_id = 'STEP1' and prev_process_id is null then 1
            when process_id = 'STEP2' and prev_process_id = 'STEP1' then 1
            when process_id = 'STEP3' and prev_process_id = 'STEP2' then 1
            when process_id = 'STEP4' and prev_process_id = 'STEP3' then 1
            when process_id = 'STEP5' and prev_process_id = 'STEP4' then 1
            else 0
        end as valid_process,
        ex_timestamp
    from tmp0
),
tmp2 as (
    select
        session_id,
        process_id,
        min(valid_process) over (
            partition by session_id
            order by ex_timestamp asc
        ) as min_valid_process
    from tmp1
)
select
    process_id as PROCESS,
    count(case when min_valid_process = 1 then session_id end) as CNT
from tmp2
group by process_id
order by process_id asc