How to reuse a sub query in sql?

Question

I have query like the following

select columns
from (select columns1
      from result_set
      where condition_common and condition1) as subset1
      join
      (select columns2
       from result_set
       where condition_common and condition2) as subset2 
      on subset1.somekey = subset2.somekey

I want to somehow reuse

select columns
from result_set
where condition_common

I have oversimplified the above query, but the above select in reality is huge and complicated. I dont want to have the burden of making sure both are in sync

I dont have any means of programmatically reusing it. T-SQL is ruled out. I can only write simple queries. This is an app limitation.

Is there a way to reuse same subquery, in a single statement

Answer 1

Use a Common Table Expression (CTE) if you're using SQL Server 2005+:

with cte as (
      select columns
      from result_set
      where condition_common
    )
select columns
from cte  as subset1
      join
      cte as subset2 
         on subset1.somekey = subset2.somekey
where otherconditions