How to perform AVG, arithmetic operations in MySQL query
You can simply use the arithmetic operators in the first SELECT 



SELECT 
   AVG(value) as value_avg1,
   AVG(value2) as value_avg2,
   AVG(value) + (5.67E-8 * POWER(AVG(value2) + 273.14, 4)) as final_value
FROM kami_all_dat
WHERE usec &gt;= 1401631200 AND usec &lt;= 1401632400