Find average and then use that value to calculate other values

Question

I have a query with a few columns. I need to find the avg of a particular column and then use the average value to calculate other values.

I am finding avg with select avg(col1) as mean from tablea. Now I want to use the mean value to calculate other values. I tried:

select avg(col1) as mean, col2 - 2(avg(col1)
from table a
group by col2. 

The problem is query should return only one row, but it is returning many rows based on col2.

Answer 1

Nest query.

SELECT col2, col2 - 2*(SELECT Avg(col1) AS mean FROM tablea) AS Calc 
FROM tablea
GROUP BY col2