select *, t2.POINT-t.AVG as DIFF, POW(t2.POINT-t.AVG, 2) as POW
from TEST_RESULTS as t2
JOIN 
(select t.USER_ID as USER_ID, COUNT(t.USER_ID) as COUNT, AVG(t.POINT) as AVG
from TEST_RESULTS as t
where t.TEST_ID = '100'
group by t.USER_ID) as t ON t2.USER_ID == t.USER_ID
where t2.TEST_ID = '100'
group by t2.USER_ID