WITH
AVG_SCORE AS (
    SELECT AVG(POINT) AS AVG_SCORE
    FROM TEST_RESULTS
    WHERE TEST_ID = '100'
)
, STDEV AS (
    SELECT SQRT(AVG((POINT - (SELECT AVG_SCORE FROM AVG_SCORE))*(POINT - (SELECT AVG_SCORE FROM AVG_SCORE)))) AS STDEV
    FROM TEST_RESULTS
    WHERE TEST_ID = '100'
)
SELECT
    USER_ID AS USER
    ,POINT AS PT
    ,CASE
        WHEN STDEV = 0
            THEN 50
        ELSE
            ROUND(50 + (POINT - AVG_SCORE.AVG_SCORE)*10/STDEV,1)
    END AS DEV_VAL
FROM TEST_RESULTS
CORSS JOIN STDEV
CORSS JOIN AVG_SCORE
WHERE TEST_ID = '100'
ORDER BY
    DEV_VAL DESC
    ,USER ASC