SQL allows a foreign-key dependency to refer to the same relation, as in the
following example:
create table manager
(employee name varchar(20) not null
manager name varchar(20) not null,
primary key employee name,
foreign key (manager name) references manager
on delete cascade )
Here, employee name is a key to the table manager, meaning that each employee
has atmost one manager. The foreign-key clause requires that every
manager also be an employee. Explain exactly what happens when a tuple
in the relation manager is deleted.
