Ambrose Bierce Many programming techniques use collection types such as arrays, bags, lists, nested tables, sets, and trees.
To support these techniques in database applications, PL/SQL provides the datatypes , which allow you to declare index-by tables, nested tables and variable-size arrays.
But you might find it impractical to store and retrieve large numbers of elements this way.
But, when you retrieve the nested table into a PL/SQL variable, the rows are given consecutive subscripts starting at 1.
That gives you array-like access to individual rows.
In this chapter, you learn how those types let you reference and manipulate collections of data as whole objects.
You also learn how the datatype is an ordered group of elements, all of the same type.