Oracle Essentials: Oracle9i, Oracle8i and Oracle8, Second Edition

Basic Data Structures

This section describes the three basic Oracle data structures: tables, views, and indexes.

Tables

The table is the basic data structure used in a relational database. A table is a collection of rows. Each row in a table contains one or more columns . If you’re unfamiliar with relational databases, you can map a table to the concept of a file or database in a nonrelational database, just as you can map a row to the concept of a record in a nonrelational database.

With the Enterprise Editions of Oracle8 and beyond, you can purchase an option called Partitioning that, as the name implies, allows you to partition tables and indexes, which are described later in this chapter. Partitioning a data structure means that you can divide the information in the structure between multiple physical storage areas. A partitioned data structure is divided based on column values in the table. You can partition tables based on the range of column values in the table, the result of a hash function (which returns a value based on a calculation performed on the values in one or more columns), or a combination of the two. With Oracle9i you can also use a list of values to define a partition, which can be particularly useful in a data warehouse environment.

Oracle is smart enough to take advantage of partitions to improve performance in two ways:

• Oracle won’t bother to access partitions that won’t contain any data to satisfy the query.

• If all the data in a partition satisfies a ...