About Collections

A collection is a PL/SQL composite variable that stores elements of the same type in a specified order, similar a one-dimensional array. The internal components of a collection are called elements. Each element has a unique subscript that identifies its position in the collection. To access a collection element, you use subscript notation: collection_name(element_subscript).

You can treat collection elements like scalar variables. You can also pass entire collections as subprogram parameters (if neither the sending nor receiving subprogram is a standalone subprogram).

A collection method is a built-in PL/SQL subprogram that either returns information about a collection or operates on a collection. To invoke a collection method, you use dot notation: collection_name.method. For example, collection_name.COUNT returns the number of elements in the collection.

PL/SQL has three types of collections:

• Associative arrays (formerly called "PL/SQL tables" or "index-by tables")

• Nested tables

• Variable arrays (varrays)

This document explains only associative arrays.