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Oracle PL/SQL Language Pocket Reference
book

Oracle PL/SQL Language Pocket Reference

by Bill Pribyl, Steven Feuerstein, Chip Dawes
April 1999
Intermediate to advanced content levelIntermediate to advanced
99 pages
2h 4m
English
O'Reilly Media, Inc.
Content preview from Oracle PL/SQL Language Pocket Reference

Collections

There are three types of collections: index-by tables (formerly known as PL/SQL tables), nested tables, and VARRAYs.

Index-by table

Single-dimension, unbounded collections of homogeneous elements available only in PL/SQL, not in the database. Index-by tables are initially sparse; they have nonconsecutive subscripts.

Nested table

Single-dimension, unbounded collections of homogeneous elements available in both PL/SQL and the database as columns or tables. Nested tables are initially dense (they have consecutive subscripts), but can become sparse through deletions.

VARRAYs

Variable-size arrays are single-dimension, bounded collections of homogeneous elements available in both PL/SQL and the database. VARRAYs are never sparse. Unlike nested tables, their element order is preserved when you store and retrieve them from the database.

The following table compares these similar collection types.

Collection Type

Characteristic

Index-by Table

Nested Table

VARRAY

Dimensionality

Single

Single

Single

Usable in SQL?

No

Yes

Yes

Usable as a column datatype in a table?

No

Yes; data stored “out of line” (in a separate table)

Yes; data typically stored “in line” (in the same table)

Uninitialized state

Empty (cannot be NULL); elements are undefined

Atomically null; illegal to reference elements

Atomically null; illegal to reference elements

Initialization

Automatic, when declared

Via constructor, fetch, assignment

Via constructor, fetch, assignment

In PL/SQL, elements ...

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Publisher Resources

ISBN: 1565924576Catalog PageErrata