Using an Alias in SQL Calculations

Why won't this query work?

SELECT 10 AS my_num, my_num*5 AS another_number
FROM table

In this example, I'm trying to use the my_num alias in other calculations. This results in unknown column "my_num"

This is a simplified version of what I am trying to do, but basically I would like to use an alias to make other calculations. My calculations are much more complicated and thats why it would be nice to alias it since I repeat it several times different ways.

Solution 1:

Simply wrap your reused alias with (SELECT alias) :

SELECT 10 AS my_num, 
       (SELECT my_num) * 5 AS another_number
FROM table

Solution 2:

You'll need to use a subselect to use that aliases that way

SELECT my_num*5 AS another_number FROM
(
    SELECT 10 AS my_num FROM table
) x