Associative arrays are analogous to conventional arrays or lists which can be defined within a PL/SQL program only. Neither the array structure nor the data can be stored in the database. It can hold the elements of a similar type in a key-value structure without any upper bound to the array. Each cell of the array is distinguished by its subscript, index, or cell number. The index can be a number or a string.
Associative arrays were first introduced in Oracle 7 release as PL/SQL tables to signify its usage within the scope of a PL/SQL block. Oracle 8 release identified the PL/SQL table as Index by table due to its structure as an index-value pair. Oracle 10g release recognized the behavior of index by tables as arrays so as to rename it as associative arrays due to association of an index with an array.
The following diagram explains the physical lookup structure of an associative array:
Associative arrays follow the following syntax for declaration in a PL/SQL declare...