10.2. Creating Indexes
The purpose of indexes can be summarized in one word: performance. An index is a database structure designed to reduce the amount of time necessary to retrieve one or more rows from a table. Indexes can also enforce uniqueness on one or more columns of a table.
index
A database object designed to reduce the amount of time it takes to retrieve rows from a table. An index is created based on one or more columns in the table.
Any number of indexes may be created on a table. An index may also be built against a combination of columns in a table; this type of index is known as a composite index.
Indexes are maintained automatically. When new rows are added to the table, new entries are recorded in the indexes. When rows are ...
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