Understanding Indexes
An index is a data structure that can greatly reduce the time it takes to find particular rows in the associated table.
A table object can have one or more indexes assigned to it. Figure 13.1 shows the syntax for creating an index on a table. Indexes can be created on one or more table columns. These columns, when relating to indexes, are known as key fields, or keys. A composite key uses more than one table column in a single index. Indexes are automatically created for the primary key constraint and can be unique—that is, have only one key value stored—or can have many keys with the same value. The more unique the key, the faster the access to the rows in the table.
Figure 13.1. SQL*Plus Help text about Create Index syntax. ...
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