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Microsoft® SQL Server 2012 Unleashed
book

Microsoft® SQL Server 2012 Unleashed

by Ray Rankins, Paul T. Bertucci, Chris Gallelli, Alex T. Silverstein
December 2013
Intermediate to advanced
1872 pages
153h 31m
English
Sams
Content preview from Microsoft® SQL Server 2012 Unleashed

Use IF EXISTS Instead of SELECT COUNT(*)

You should use IF EXISTS instead of SELECT COUNT(*) when checking only for the existence of any matching data values and when determining the number of matching rows is not required. IF EXISTS stops the processing of the select query as soon as the first matching row is found, whereas SELECT COUNT(*) continues searching until all matches are found, wasting I/O and CPU cycles. For example, you could replace

if (SELECT count(*) FROM Sales.SalesOrderDetail WHERE ProductID = 324) > 0

with an IF EXISTS check similar to

if EXISTS (SELECT * FROM Sales.SalesOrderDetail WHERE ProductID = 324)

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Publisher Resources

ISBN: 9780133408539Purchase book