WITH Stats AS (
    SELECT 
        AVG(POINT) AS Mean,
        SQRT(AVG((POINT - AVG(POINT)) * (POINT - AVG(POINT)))) AS StdDev
    FROM TEST_RESULTS
    WHERE TEST_ID = '100'
)

SELECT 
    TR.USER_ID AS USER, 
    TR.POINT AS PT,
    CASE 
        WHEN StdDev = 0 THEN 50 
        ELSE ROUND((10 * (TR.POINT - Mean) / StdDev) + 50, 1) 
    END AS DEV_VAL
FROM TEST_RESULTS TR, Stats
WHERE TR.TEST_ID = '100'
ORDER BY DEV_VAL DESC, USER ASC;