In Oracle, the collection typed value is encapsulated. Consequently, a user must access
the contents of a collection via interfaces provided by Oracle. Generally, when the user
accesses a nested table, Oracle returns the entire collection value to the user’s client
process. This may have performance implications, and so Oracle supports the ability to
return a nested table value as a locator, which is like a handle to the collection value. The
RETURN AS LOCATOR clause indicates that the nested table is to be returned in the
locator form when retrieved. If this is not specified, the default is VALUE, which indicates
that the entire nested table is to be returned instead of just a locator to the nested table.
Nested tables differ from arrays in the following ways: