select * from dept d
where  not exists 
  (select /*+ no_unnest */'x' from emp where deptno = d.deptno);
  
select * from dept d
where  not exists 
  (select /*+ unnest nl_aj */'x' from emp where deptno = d.deptno);

select * from dept d
where  not exists 
  (select /*+ unnest merge_aj */ 'x' from emp where deptno = d.deptno);

select * from dept d
where  not exists 
  (select /*+ unnest hash_aj */ 'x' from emp where deptno = d.deptno);
  
