Describe queries with complex types?

The present extension of the SQL query language deal with the complex type

Let us start with the simple example:

Find the title and the name of the publisher of each book this query carries out the task:

Select title, publisher.name

From books

path expression

The reference are dereference in 1999 by the -> simple

Select head-> name, head->address

From dept

An expression such as" head->name" is called the path expression.

Collection valued attributes

Nesting and unnesting

The transformation of the nested relation in to a form with fewer (or no) the relation -valued attribute value is known as unnesting

The reverse process of transformation a INF relation into a nested relation is known as nesting.