Updating nested table
To look up data that is more complex than single values, you can store PL/SQL records or SQL object types in collections.Nested tables and varrays can also be attributes of object types.Nested tables can be sparse: you can delete arbitrary elements, rather than just removing an item from the end.Nested table data is stored out-of-line in a store table, a system-generated database table associated with the nested table.You must update or retrieve all elements of the varray at the same time, which is most appropriate when performing some operation on all the elements at once.But you might find it impractical to store and retrieve large numbers of elements this way.
Varrays are a good choice when the number of elements is known in advance, and when the elements are usually all accessed in sequence.
Within the database, nested tables can be considered one-column database tables.
Oracle stores the rows of a nested table in no particular order.
When stored in the database, varrays retain their ordering and subscripts.
Each varray is stored as a single object, either inside the table of which it is a column (if the varray is less than 4KB) or outside the table but still in the same tablespace (if the varray is greater than 4KB).