Question

I am stuck at one point of the book “SQL and Relational Theory”, which pertains to the types that relational attributes can take. The question is this:

There are exceptions to the rule that relational attributes can be of any type whatsoever, of which one is that if a relation R is of type
T, then attributes of R cannot themselves be of type T.

Why? Is it because the relation R will be of a type ‘Relation [name]’, and so attributes cannot be of this type?

Answer 1

Consider something like this:

create table address {
    id int,
    name varchar(20),
    details address -- the address relation has an attribute that is another of itself
}

The definition would recurse infinitely.