WITH DEV(val, avrg) AS 
    (SELECT sqrt(AVG(pw)), av FROM
    (SELECT (POINT - av) * (POINT - av) AS pw, av
        FROM TEST_RESULTS CROSS JOIN (SELECT AVG(POINT) AS av FROM TEST_RESULTS WHERE TEST_ID = '100')  WHERE TEST_ID = '100'))

SELECT
    USER_ID AS USER,
    POINT AS PT,
    (CASE DEV.val
        WHEN 0 THEN 50
        ELSE ROUND((POINT - avrg) * 10 / DEV.val + 50 , 1)
    END) AS DEV_VAL
FROM
    TEST_RESULTS CROSS JOIN DEV
WHERE
    TEST_ID = '100'
ORDER BY
    DEV_VAL DESC, USER_ID;