What is an index?

 Posted by Karthikanbarasan on 1/8/2011 | Category: Sql Server Interview questions | Views: 6535 | Points: 40

? An index is a physical structure containing pointers to the data.
? Indices are created in an existing table to locate rows more quickly and efficiently.
? It's possible to create index on one or more columns of a table, and each index is given a name.
? The users cannot see the indexes; they are just used to speed up queries.
? Effective indexes are one of the best ways to improve performance in a database application.
? A table scan happens when there is no index available to help a query. In a table scan SQL Server examines every row in the table to satisfy the query results.
? Table scans are sometimes unavoidable, but on large tables, scans have a terrific impact on performance.

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