Nested Tables

1.   A nested table in Oracle is a collection type that can store an unbounded number of elements, unlike VARRAYs which have a fixed maximum size.

2.   Nested tables are initially dense but can become sparse when elements are deleted, meaning index values may have gaps.

3.   They can be stored in database tables as a column, where Oracle internally manages them using a separate storage table.

4.   Nested tables can be queried and manipulated using SQL by treating them like a relational table with the TABLE() operator.

5.   Elements in a nested table do not preserve a guaranteed physical order when stored in the database unless explicitly ordered in queries.

6.   Nested tables support set-level operations such as UNION, INTERSECT, and MULTISET operators, making them useful for complex data processing.

7.   You can add or remove elements dynamically from a nested table using EXTEND, DELETE, and TRIM methods.

8.   Nested tables can be used as parameters and return types in PL/SQL functions and procedures for passing multiple values.

9.   Unlike associative arrays, nested tables can be stored persistently in the database and accessed directly from SQL statements.

10.                   Nested tables are suitable for large and variable-sized collections but may have higher overhead compared to VARRAYs due to separate storage management.