/* What are the suppliers that supply all parts using NOT EXISTS */
/* sp difference A */
select DISTINCT snumber
from spj as c
where not EXISTS 
/* A */
/* Cross Product */
(select DISTINCT b.snumber
 from part as a cross join spj as b 
 where c.snumber = b.snumber and not EXISTS
 /* difference cross product sp */
 (select snumber, pnumber from spj
  where b.snumber = spj.snumber and a.pnumber = spj.pnumber));

  
  /* What are the suppliers that supply all parts using NOT EXISTS * */
/* sp difference A */
select DISTINCT snumber
from spj as c
where not EXISTS 
/* A */
/* Cross Product */
(select *
 from part as a cross join spj as b 
 where c.snumber = b.snumber and not EXISTS
 /* difference cross product sp */
 (select * from spj
  where b.snumber = spj.snumber and a.pnumber = spj.pnumber));
  
  
/* What are the suppliers that supply all parts using NOT EXISTS *, list their names and their cities */
select snumber, sname, city from supplier
WHERE snumber in
(/* sp difference A */
select DISTINCT snumber
from spj as c
where not EXISTS 
/* A */
/* Cross Product */
(select *
 from part as a cross join spj as b 
 where c.snumber = b.snumber and not EXISTS
 /* difference cross product sp */
 (select * from spj
  where b.snumber = spj.snumber and a.pnumber = spj.pnumber)));