A homogeneous single dimension data structure which is made up of elements of same datatype is called collection in Oracle Database. In simple language we can say that, an array in Oracle Database is called Collection.
The structure of PL/SQL collections consist of a cell with subscript called index. Data is stored into these cells and can be identified and accessed using the index number. This is again very similar to the structure of arrays, but unlike array PL/SQL Collections are strictly one-dimensional.
PL/SQL collections can be divided into two categories:
1. Persistent (Nested tables and VARRAY)
2. Non-persistent.(Associative Array)
