Abfragen
========
where exists (tupel)
where not exists (tupel)
where X < (wert)
where X < any (tupel)
where X < all (tupel)
where X in (tupel)
(case when x<1 then 'a'
when x<2 then 'b'
else 'c'
end)
Integrität
==========
x integer primary key
foreign key (tuple) references table
on delete cascade/set null, on update cascade/set null
Semester integer check Semester between 1 and 13
Rang char(2) check (Rang in ('C2','C3','C4'))
constraint Name
check (exists ( select...) )
trigger -> echter code