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Microsoft® SQL Server 2012 Unleashed by Alex T. Silverstein, Chris Gallelli, Paul T. Bertucci, Ray Rankins

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Poor Index Design

Poor index design is another reason—often a primary reason—why queries might not optimize as you expect them to. If no supporting indexes exist for a query, or if a query contains SARGs that cannot be optimized effectively to use the available indexes, SQL Server ends up performing either a table scan, an index scan, or another hash or merge join strategy that is less efficient. If this appears to be the problem, you need to re-evaluate your indexing decisions or rewrite the query so it can take advantage of an available index. For more information on designing useful indexes, see Chapter 30.

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