with base as (
select
    SESSION_ID
    ,cast(replace(PROCESS_ID,"STEP","") as int) as PROCESS_ID
    ,row_number() over (partition by SESSION_ID order by EX_TIMESTAMP) as PR_ORDER
    ,EX_TIMESTAMP
from
    PROCESS_LOG
)
,base2 as (
select
    SESSION_ID
    ,PROCESS_ID
    ,EX_TIMESTAMP
    ,row_number() over (partition by SESSION_ID order by EX_TIMESTAMP) as PR_ORDER2
from
    base
where
    PROCESS_ID = PR_ORDER
)
select
    "STEP"||PROCESS_ID as PROCESS
    ,count(distinct SESSION_ID) as CNT
from
    base2
where
    PROCESS_ID = PR_ORDER2
group by 
    PROCESS_ID
order by
    PROCESS_ID