SQL Server query optimizer uses statistics to create query plans that improve query performance. For most queries, the query optimizer already generates the necessary statistics for a high quality query plan; in a few cases, you need to create additional statistics or modify the query design for best results. By default, SQL Server maintains statistics for index columns. You can also keep statistics on selected non-indexed columns, if desired. Statistics on non-indexed columns count toward the limit of non-clustered indexes (249) that you can have on a table.
Checkout my article here, in which you’ll learn what query optimisation statistics are and how SQL Server query optimizer uses statistics. You will also learn how to create and manage statistics, and what are the different ways to determine when statistics were last updated in SQL Server.
This article is published on SQL-SERVER-PERFORMANCE.COM.