Given a Relation POSITION (Posting-No, Skill), then query to retrieve all distinct pairs of posting-nos requiring skill is
1.Select p1.posting-No, p2.posting-No from position p1, position p2 where p1.skill = p2.skill and p1.posting-No = p2.posting.No;
2. Select p1.posting-No, p2.posting-No from position p1, position p2 where p1.skill = p2.skill and p1.posting-No < p2.posting-No;
3.Select p.posting-No, p.posting-No from position p where p.skill = p.skill and p.posting-No < p.posting-No;
4. Select p1.posting-No, p2.posting-No from position p1, position p2 where p1.skill = p2.skill;