Considerando as tabelas R e S apresentadas anteriormente,...

select * from R

where not exists (select * FROM S where a=c)

select * from R

where not exists (select * FROM S where a=d)

select * from S

where not exists (select * FROM R where a=c)

select * from S

where not exists (select * FROM R where a=d)

select * from R

where exists (select * FROM S where b=d)