How to sum two aliased values in a query

[Ig Ta]

First of all sorry for my english but I hope someone can help me
in my problem.

I need to sum two aliased values in a query in order to order
the results.

The query looks like this:

SELECT t1.ID, t2.name1, t2.name2
COUNT(DISTINCT t3.pos > '10') AS res_1,
SUM(IF(t4.points = 'val' AND
t3.pos = $t4.val)) AS res_2,

till this point it's all ok, but when I try to sum the
two aliased values res_1 and res_2 I always get '0'
as result...

(IFNULL('res_1', 0) + IFNULL('res_2',0)) AS total

FROM
t1, t2, t3, t4

I tried it also with variables but I always got the
same result