SQL Reference

Indexes

An index is an ordered set of pointers to rows of a base table. Each index is based on the values of data in one or more table columns. An index is an object that is separate from the data in the table. When an index is created, the database manager builds this structure and maintains it automatically.

Indexes are used by the database manager to:

• Improve performance. In most cases, access to data is faster than without an index.

  An index cannot be created for a view. However, an index created for a table on which a view is based may improve the performance of operations on the view.

• Ensure uniqueness. A table with a unique index cannot have rows with identical keys.