SELECT
    USER_ID AS USER
    ,POINT AS PT
    ,ROUND((((POINT - AVERAGE)*10)/sd) + 50,2) AS DEV_VAL
FROM TEST_RESULTS
CROSS JOIN
(
SELECT
    SQRT(AVG(sd)) as sd
    ,AVERAGE
FROM
(
            SELECT
            *
            ,AVERAGE
            ,(POINT - AVERAGE)*10 AS Diff
            ,(POINT - AVERAGE)*(POINT - AVERAGE) AS sd
        FROM TEST_RESULTS
        CROSS JOIN
        (
            SELECT
                AVG(POINT) AS AVERAGE 
            FROM TEST_RESULTS
            WHERE TEST_ID =100
        )
        WHERE TEST_ID =100
)
WHERE TEST_ID =100
)
WHERE TEST_ID =100