Differences Between VARRAY, Nested Table, and Associative Array in PL/SQL

1. VARRAY (Variable-Sized Array):

Fixed size: You must specify the maximum number of elements it can hold at the time of declaration.

Stored in a contiguous memory block, making it efficient for small collections.

Elements are always stored in the order they are inserted, and indexing starts from 1.

Suitable when the maximum number of elements is known and doesn't change often.

1. Nested Table:

Can grow dynamically without a predefined maximum size.

Initially, it can be dense (without gaps), but after deletions, it can become sparse (with gaps).

Elements are stored out-of-line in a separate table, which allows for easy querying and manipulation.

Useful when working with large collections or when elements need to be stored in the database.

1. Associative Array (Index-By Table):

No fixed size; it can dynamically grow and shrink.

Indexed by either integers or strings, allowing flexibility in accessing elements.

Stored entirely in memory, and elements are not necessarily stored in order.

Best for temporary data manipulation where you need quick lookups by key, but it’s not directly stored in the database.

Summary:

VARRAY: Fixed size, ordered, efficient, but limited in scalability.

Nested Table: Dynamically sizable, can be sparse, can be stored in and queried from the database.

Associative Array: Dynamically sizable, indexed by custom keys, ideal for in-memory operations, not directly storable in the database.