Nested tables are a persistent form of collections which can be created in the database as well as PL/SQL. It is an unbounded collection where the index or subscript is implicitly maintained by the Oracle server during data retrieval. Oracle automatically marks the minimum subscript as
1 and relatively handles others. As there is no upper limit defined for a nested table, its size can grow dynamically. Though not an index-value pair structure, a nested table can be accessed like an array in a PL/SQL block.
A nested table is initially a dense collection but it might become sparse due to delete operations on the collection cells.
Dense collection is the one which is tightly populated. That means, there exists no empty cells between ...