select
user_id as USER,
point as PT, 
case when stdev = 0 then 50
else round((((point- average)*10)/ stdev)+50,1) end as DEV_VAL
from test_results
cross join (
select
average,
sqrt(avg(pow(point-average,2))) as stdev
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'
order by DEV_VAL desc,user_id;