select
    ID,
    sum(A) as A1,
    sum(B) as B1,
    sum(A-B) as razn
from
(
select
    ID,
    sum(f1) as A,
    cast(0 as float) as B
     from t1
       group by ID
union all
select
    ID,
    cast(0 as float),
    sum(f2) as B
     from t2
       group by ID) as dt1
group by ID

SELECT elj.job_code,
       elj.job_title
FROM   ( SELECT job_code,
                job_title
         FROM   job
         WHERE  max_salary < 50000 ) AS elj;

The following is a more complex statement using derived tables:
SELECT emp.emp_no,
       emp.full_name,
       emp.job_code,
       job.job_grade,
       job.job_title
FROM   ( SELECT emp_no,
                full_name,
                job_code,
                job_grade,
                job_country
         FROM   employee ) AS emp,
       ( SELECT job_code,
                job_grade,
                job_country,
                job_title
         FROM   job ) AS job
WHERE  ( emp.job_code = job.job_code ) AND
       ( emp.job_grade = job.job_grade ) AND
       ( emp.job_country = job.job_country ) AND
       ( emp.job_country = 'USA' );

select
    G.ID,
    G.NAME,
    dt2.A1 as INC,
    dt2.B1 as SALES,
    dt2.ostatok as RESTS
FROM Good g 
Join
 (select
    ID,
    sum(A) as A1 ,
    sum(B) as B1,
    sum(A-B) as ostatok
  from
      (select
         ID,
         sum(f1) as A,
         cast(0 as float)as B
          from t1
           group by ID
       union all
       select
         ID,
         cast(0 as float),
         sum(f2) as B
          from t2
           group by ID) as  dt1
   group by ID)as dt2
On G.ID=dt2.ID
Order by G.Name