Indexinggreenspun.com : LUSENET : DBAzine : One Thread
Please explain me how the indexes are useful in database and also tell me how index are used.
Thanks and Regards
-- SIVALINGAM SATHYAMURTHY (firstname.lastname@example.org), December 03, 2002
This is a very high level question, so I'm going to give you a very high level answer. More details can be found in my book, Database Administration (http://www.amazon.com/exec/obidos/ASIN/0201741296/mullinassoci- 20/103-4851251-5332609).
An index provides an alternate path to data in the database. Fewer I/Os are required to search an index than to search every record in the database. This is so because the index is ordered by a specific key and index entries are much smaller than the database rows. By reducing I/O we improve query performance.
Relational indexes are automatically maintained so that whenever new data is inserted to the database, or when data is modified, the relevant index entries are also modified. This makes the indexes always useful for querying.
This answer is necessarily high level and brief given the nature of the question.
-- Craig S. Mullins (email@example.com), January 16, 2003.