WITH STEP1 AS (
    SELECT
        SESSION_ID
        , EX_TIMESTAMP
    FROM
        PROCESS_LOG
    WHERE
        PROCESS_ID = 'STEP1'
),
STEP1AFR AS (
    SELECT
        a.SESSION_ID
        , ROW_NUMBER() OVER (PARTITION BY a.SESSION_ID) AS RNUM
        , PROCESS_ID
        , CAST(REPLACE(PROCESS_ID, 'STEP', '') AS INT) AS PROCNUM
        , a.EX_TIMESTAMP
    FROM
        PROCESS_LOG a
        INNER JOIN STEP1 b ON
            a.SESSION_ID = b.SESSION_ID
            AND a.EX_TIMESTAMP >= b.EX_TIMESTAMP
),
MAXPROC AS (
    SELECT
        SESSION_ID
        , MAX(PROCNUM) AS PROC
    FROM
        STEP1AFR
    WHERE
        RNUM = PROCNUM
    GROUP BY
        SESSION_ID
)
SELECT
    'STEP' || PROC AS PROCESS
    , COUNT(SESSION_ID) AS CNT
FROM
    MAXPROC
GROUP BY
    PROC
;