SELECT
    PROCESS_ID AS PROCESS,
    COUNT(SESSION_ID) AS CNT
FROM (
    SELECT
        SESSION_ID,
        PROCESS_ID,
        SUBSTRING(PROCESS_ID,5,1) AS STEPNO,
        RANK()OVER(PARTITION BY SESSION_ID ORDER BY EX_TIMESTAMP ASC) AS TIMENO
    FROM PROCESS_LOG
    )
WHERE
    CAST(STEPNO AS INTEGER) = TIMENO
GROUP BY
    PROCESS
ORDER BY
    PROCESS