with T as (
    select
        AVG(POINT) as me,
        SQRT(AVG(POINT*POINT)-AVG(POINT)*AVG(POINT)) as std
    from TEST_RESULTS where  TEST_ID='100'
)
select user_id as USER,
       point as PT,
       case when std=0.0 then 50 else round((point - me)*10/std + 50,1) end as DEV_VAL
from TEST_RESULTS, T
where TEST_RESULTS.TEST_ID='100'
order by 3 desc,1