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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

Estimating Access Path Cost

After the selectivity of each of the SARGs, OR clauses, and join clauses is determined, the next phase of optimization is estimating the access path cost of the query. The Query Optimizer attempts to identify the total cost of various access paths to the data and determine which path results in the lowest cost to return the matching rows for an expression.

The primary cost of an access path, especially for single-table queries, is the number of logical I/Os required to retrieve the data. Using the available statistics and the information stored in SQL Server regarding the average number of rows per page and the number of pages in the table, the Query Optimizer estimates the number of logical page reads necessary to ...

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Publisher Resources

ISBN: 9780768696585Purchase book