An index is a schema object that contains an entry for each value that appears in the indexed column(s) of the table or cluster and provides direct, fast access to rows. Oracle Database supports several types of index: Normal indexes. (By default, Oracle Database creates B-tree indexes.)
Advantage of Indexes in SQL Server
The database engine can use indexes to boost performance in a number of different queries. Sometimes these performance improvements are dramatic. An important feature of SQL Server 2000 is a component known as the query optimizer. The query optimizer's job is to find the fastest and least resource intensive means of executing incoming queries. An important part of this job is selecting the best index or indexes to perform the task. In the following sections we will examine the types of queries with the best chance of benefiting from an index.
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