with q1 as(
 select Nomer from dual
 union 
 select Nomer from dual
), GO as(
 select nomer, fil from t1
 join t2 on t1.a = t2.a
),  FIL1 as
 select nomer, fil from t1
 join t3@dblink on t1.a = t3.a
)
select qwe
from GO 
join table on GO.nomer = table.nomer

union  /*как только я добавляю union к удаленной таблице запрос начинает ужасно долго выполняться*/
select qwe
from FIL1 
join table2@dblink on FIL.nomer = table2.nomer

with q1 as(
 select Nomer from dual
 union 
 select Nomer from dual
), GO as(
 select nomer, fil from t1
 join t2 on t1.a = t2.a
),  FIL1 as
 select nomer, fil from t1
 join t3@dblink on t1.a = t3.a
)
select qwe
from GO 
join table on GO.nomer = table.nomer

union  
select /*+ DRIVING_SITE(t2)*/ 
        qwe
from FIL1 f
join table2@dblink t2 on FIL.nomer = table2.nomer