select * 
from t
where t.id in (select t.id
               from t
               where ...
               group by t.id
               having count(*) = 2)
/
select t1.*
from t t1,
     (select t.id
      from t
      where ...
      group by t.id
      having count(*) = 2) t2
where t1.id = t2.id 
/
select * from t where <one condition>
intersect 
select * from t where <another condition>
/
select *
from (select t.*,
             sum(case when <conditions> then 1 end) 
               over (partition by t.id) cnt
      from t)
where cnt = 2
/

 select candidateid from 
(select candidateid,count(distinct skillid) cnt 
 from skill where 
 skillid in ('1','2') 
 group by candidateid) 
where cnt=2