O'Reilly logo

Microsoft SQL Server 2014 Unleashed by Paul Bertucci, Alex T. Silverstein, Chris Gallelli, Ray Rankins

Stay ahead with the world's most comprehensive technology and business learning platform.

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, tutorials, and more.

Start Free Trial

No credit card required

Estimating Access Path Cost

After the selectivity of each of the SARGs, OR clauses, and join conditions is determined, the next phase of optimization is estimating the access path cost of each search or join expression. 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 ...

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, interactive tutorials, and more.

Start Free Trial

No credit card required