An associative array is a non-persistent unbounded collection which means that an associative array cannot be created in the Oracle Database schema, but locally declared within the declarative section of a PL/SQL block.
A nested table is a persistent collection of homogeneous elements that can be created in a database as a schema object as well as declared within a PL/SQL block. A nested table being an unbounded collection, has no limit on the number of elements.
A varray is a single-dimensional homogeneous collection that can be created in a database as well as in PL/SQL. Being a bounded collection, it can hold only a fixed number of elements.
