WITH 
S_ROW AS
(
SELECT SESSION_ID,PROCESS_ID,EX_TIMESTAMP,ROW_NUMBER() OVER (PARTITION BY SESSION_ID ORDER BY EX_TIMESTAMP ASC) ROW FROM
PROCESS_LOG 
),
FILTER_NUM AS
(
SELECT SESSION_ID, MIN(ROW) LIMIT_NO,PROCESS_ID
FROM S_ROW
WHERE PROCESS_ID != 'STEP'||ROW
GROUP BY SESSION_ID
),
FILTER_ROW AS
(
SELECT SESSION_ID,ROW,PROCESS_ID FROM S_ROW
WHERE PROCESS_ID = 'STEP'||ROW
)

SELECT R.PROCESS_ID,COUNT(R.PROCESS_ID) CNT
FROM
    FILTER_ROW R
LEFT JOIN
    FILTER_NUM N ON R.SESSION_ID = N.SESSION_ID
WHERE LIMIT_NO IS NULL OR ROW < LIMIT_NO
GROUP BY R.PROCESS_ID
ORDER BY R.PROCESS_ID ASC