SUM() 3 columns with alias into a fourth one This is one part of my procedure:

 select nome, 

       --casos expedidos (- 3 meses)
       isnull((SELECT      count(cod_rep)    
                    FROM   tbReps 
                    where  tbreps.cod_status = 7
                    and          tbreps.cod_perito_primeiro=cod_usuario
                    AND          (MONTH(tbreps.datahora_emissao) = MONTH(@DATA1) 
                    AND          YEAR(TBREPS.datahora_emissao) = YEAR(@DATA1))),0) as Laudos_Expedidos1,


       --casos expedidos (- 2 meses)
       isnull((SELECT      count(cod_rep)    
                    FROM   tbReps 
                    where  tbreps.cod_status = 7
                    and          tbreps.cod_perito_primeiro=cod_usuario
                    AND          (MONTH(tbreps.datahora_emissao) = MONTH(@DATA2)
                    AND          YEAR(TBREPS.datahora_emissao) = YEAR(@DATA2))),0) as Laudos_Expedidos2,



       --casos expedidos (- 1 meses)
       isnull((SELECT      count(cod_rep)    
                    FROM   tbReps 
                    where  tbreps.cod_status = 7
                    and          tbreps.cod_perito_primeiro=cod_usuario
                    AND          (MONTH(tbreps.datahora_emissao) = MONTH(@DATA3)
                    AND          YEAR(TBREPS.datahora_emissao) = YEAR(@DATA3))),0) as Laudos_Expedidos


It will create this:



How can I sum, for example, LAUDOS_EXPEDIDOS1 + LAUDOS_EXPEDIDOS2  Into a 4º column? like this:

 

I'm pretty sure it's something really easy. I'm trying to use sum with the aliases, with no success.
You cannot refer to an alias defined in the same SELECT list. There are various workarounds. Assuming your query is something like this:

select nome, 
       -- various complex expression / subqueries
       &lt;complex_expression_or_subquery&gt;
           as Laudos_Expedidos,
       &lt;complex_expression_or_subquery&gt;
           as Laudos_Expedidos2
from &lt;table_name&gt; ;



Duplicate code. As this is the least attractive solution, for various reasons, I won't add a code sample. 
a derived table or a CTE allows to use the aliases as they are already defined in a previous level:

with cte as
( select nome, 
         -- various complex expression / subqueries
         &lt;complex_expression_or_subquery&gt;
             as Laudos_Expedidos,
         &lt;complex_expression_or_subquery&gt;
             as Laudos_Expedidos2
  from &lt;table_name&gt;
) 
select c.*,
       c.Laudos_Expedidos + c.Laudos_Expedidos2
           as Total_Laudos_Expedidos
from cte as c ;

Use CROSS / OUTER APPLY allows also to refer to previously defined aliases. This offers the possibility of using multiple outer/cross apply subqueries, if you want to use the aliases of the first apply in further calculations. (With the derived/CTE solution, that is also possible but the code usually looks more complicated):

select t.nome, 
       f.*,
       g.Total_Laudos_Expedidos,
       f.Laudos_Expedidos / g.Total_Laudos_Expedidos
           as Percent_Expedidos
from &lt;table_name&gt; as t
  outer apply
    ( select 
          -- various complex expression / subqueries
          &lt;complex_expression_or_subquery&gt;
              as Laudos_Expedidos,
          &lt;complex_expression_or_subquery&gt;
              as Laudos_Expedidos2
    ) as f 
  outer apply
    ( select 
          f.Laudos_Expedidos + f.Laudos_Expedidos2
              as Total_Laudos_Expedidos   
    ) as g ;