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.