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Collection is an ordered group of elements, all of the same type (for example, the grades for a class of students). Each element has a unique subscript that determines its position in the collection. PL/SQL offers three kinds of collections: associative arrays, nested tables, and varrays (short for variable-size arrays). Nested tables extend the functionality of associative arrays (formerly called "PL/SQL tables" or "index-by tables").

Collections work like the arrays found in most third-generation programming languages. Collections can have only one dimension. Most collections are indexed by integers, although associative arrays can also be indexed by strings. To model multi-dimensional arrays, you can declare collections whose items are other collections.

Nested tables and varrays can store instances of an object type and, conversely, can be attributes of an object type. Collections can also be passed as parameters. You can use them to move columns of data into and out of database tables or between client-side applications and stored subprograms.

New collections are created within Create Collection Wizard. In order to run the wizard you should either

•	select the Object \| Create Database Object... main menu item;

•	select the Collection icon in the Create Database Object dialog

•	select the Collection list or any object from that list in the explorer tree;

•	select the Create New Collection... item from the popup menu

•	open the schema in Schema Editor and the Collection tab there;

•	press the Insert key or select the Create New Collection item from the popup menu (alternatively, you may use the corresponding link of the Navigation Bar).

To create a new collection with the same properties as one of the existing collection has:

•	select the Object \| Duplicate Database Object... main menu item;

•	follow the instructions of Duplicate Object Wizard.

Collections can be edited within Collection Editor. In order to run the editor you should either

•	select the collection for editing in the explorer tree (type the first letters of the

collection name for quick search);

•	select the Edit Collection ... item from the popup menu

•	open the schema in Schema Editor and the Collection tab there;

•	select the collection to edit;

•	press the Enter key or select the Edit Collection item from the popup menu (alternatively, you may use the corresponding link of the Navigation Bar).

To drop a collection:

•	select the collection to drop in the explorer tree;

•	select the Drop Collection item from the popup menu

•	open the schema in Schema Editor and the Collection tab there;

•	select the collection to drop;

•	press the Delete key or select the Drop Collection item from the popup menu (alternatively, you may use the corresponding link of the Navigation Bar)

and confirm dropping in the dialog window.