select S#,SNAME
from S
where S.S# in(select SC.S#
			  from SC
			  where C#='C2');
			  			  
select S#,SNAME
from S
where S.S# in(select SC.S#
			  from SC
			  where SC.C# in(select C.C#
							 from C
							 where CNAME='MATHS'));
							 
select SNAME,AGE
from S
where S# not in(select S#
				 from SC
				 where C#='C2');
				 
select SNAME
from S
where S# in(select S#
			from SC
			GROUP BY S#
			HAVING count(SC.C#) in(select count(C.C#)
								   from C));