New field based on sum field

I'm trying to create a new field based in another (sum field) SELECT sum(price) AS old_price, old_price+100 AS total_price FROM sales This returns **Unknown column 'old_price' in 'field list'** sum is just a example, my real issue is to use with a select inside this field What am I doing wrong? Thanks. --edit I've used variables to reuse the alias, updated code: SELECT @old_price := sum(price) AS old_price, @old_price+100 AS total_price FROM sales If you think that it is not a good practice, tell me.