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Microsoft® SQL Server 2008 R2 Unleashed
book

Microsoft® SQL Server 2008 R2 Unleashed

by Ray Rankins, Paul Bertucci, Chris Gallelli, Alex T. Silverstein
September 2010
Intermediate to advanced content levelIntermediate to advanced
1704 pages
111h 8m
English
Sams
Content preview from Microsoft® SQL Server 2008 R2 Unleashed

Index Covering

Index covering is a situation in which all the information required by the query in the SELECT and WHERE clauses can be found entirely within the nonclustered index itself. Because the nonclustered index contains a leaf row corresponding to every data row in the table, SQL Server can satisfy the query from the leaf rows of the nonclustered index. This results in faster retrieval of data because all the information can come directly from the index page, and SQL Server avoids lookups of the data pages.

Because the leaf pages in a nonclustered index are linked together, the leaf level of the index can be scanned just like the data pages in a table. Because the leaf index rows are typically much smaller than the data rows, a nonclustered ...

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Publisher Resources

ISBN: 9780768696585Purchase book