Find the id of students who do not have a cat pet.
create table has_pet (stuid varchar, petid varchar, PRIMARY KEY (stuid)); create table pets (petid varchar, pettype varchar, PRIMARY KEY (petid)); create table student (stuid varchar, PRIMARY KEY (stuid))
select stuid from student except select t1.stuid from student as t1 join has_pet as t2 on t1.stuid = t2.stuid join pets as t3 on t3.petid = t2.petid where t3.pettype = 'cat'