--select nom, prenom from employe where empno not in(select distinct chef from employe where chef is not null);
--select nom, prenom from employe where empno !=all(select distinct chef from employe where chef is not null);
--select distinct e.nom, e.prenom from employe e, employe c where e.empno=c.chef(+) and c.chef is null; --jointure externe
--select nom, prenom from employe e where not exists(select * from employe where e.empno=chef);
--select empno from employe minus (select distinct chef from employe);


--select nom, prenom from employe e where e.chef is null and exists(select * from employe where e.empno=chef); 


--select nom, prenom from employe where empno in(select distinct chef from employe);


select distinct e.nom, e.prenom from employe e, employe c where e.empno=c.chef(+) and c.chef is not null and e.salaire > c.salaire;

