There are three types of collections in the Oracle Database 10g family of products. They are the VARRAY, NESTED TABLE, and associative array data types.
VARRAY and NESTED TABLE are both SQL and PL/SQL data types. As SQL data types, they can define user-specified column data types. Both of the VARRAY and NESTED TABLE data types are structures indexed by sequential integers. Sequentially indexed structures disallow gaps in the index values, and are also known as densely populated structures. While the VARRAY has a fixed number of elements when defined, the NESTED TABLE does not.
The associative array, previously known as a PL/SQL table, is only a PL/SQL data type. Associative array data types can only be referenced in a PL/SQL scope. ...