To look up data that is more complex than single values, you can store PL/SQL records or SQL object types in collections.
You also learn how the datatype is an ordered group of elements, all of the same type.
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.
PL/SQL nested tables are like one-dimensional arrays.
You can model multi-dimensional arrays by creating nested tables whose elements are also nested tables.