create table Stadare (
	snr integer,
	namn varchar(10),
	timkostnad integer,
	primary key (snr));

create table Yta (
	ynr integer,
	beskrivning varchar(10),
	area integer,
	stadare integer,
	primary key (ynr),
	foreign key (stadare) references Stadare (snr));

insert into Stadare values (1, 'Hjalmar', 100);
insert into Stadare values (2, 'Hulda', 150);
insert into Stadare values (3, 'Saddam', 100);
insert into Stadare values (4, 'Saddam', 1000);

insert into Yta values (10, 'T1', 2000, 1);
insert into Yta values (20, 'T2', 2000, 1);
insert into Yta values (30, 'T3', 2000, 2);
insert into Yta values (40, 'X1', 100, 2);
insert into Yta values (50, 'X2', 100, null);

select * from Stadare;
select * from Yta;

select * from Yta, Stadare
where Yta.stadare = Stadare.snr
and Yta.beskrivning = 'T1';

select * from Yta
where stadare is null;

select * from Stadare
where snr not in (select stadare from Yta);

select * from Stadare                                                
where snr not in (select stadare from Yta where stadare is not null);

select snr, namn
from Stadare, Yta
where Stadare.snr = Yta.stadare
group by snr, namn
having sum(area) > 40 * 60;