Comments on: Tips on Optimizing SQL Server Composite Indexes http://www.sql-server-performance.com/2007/composite-indexes/ SQL Server Performance Tuning Fri, 14 Jun 2013 19:09:55 +0000 hourly 1 http://wordpress.org/?v=3.5.1 By: Darton Williams http://www.sql-server-performance.com/2007/composite-indexes/#comment-1910 Darton Williams Thu, 10 May 2012 14:51:41 +0000 http://www.sql-server-performance.com/?=209#comment-1910 I’ve found that correct composite indexes can make a huge difference in performance when joining multiple tables and filtering on several columns. I have a query joining three tables, two of which contain only foreign keys. The largest one has ~32000 rows, so not a huge database.

This query, returning 600 rows, took over 7 minutes to run when I first began testing. The execution plan did not show any table scans and all single-key indexes were being used. Rewriting the query helped, but it still took minutes. Adding two composite indexes on each foreign key table decreased execution time to < 1 second.

Strangely, the execution plan did not show much of a change in relative time spent on the formerly slow join to the rest of the query.

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