“SQL Server Statistics” from Simple-Talk
Holger Schmeling’s work in SQL Server Distribution Statistics was first published as a pair of long articles for Simple-Talk. The booklet takes a practical, and well-informed approach to a subject that is not always easy to explain or understand. A Distribution Statistics object is a sampled map of the distribution of data in a table. Such statistics help the Query Optimizer of SQL Server’s Database Engine to translate the ‘logical’ SQL Query into the best strategy for doing all the physical operations of joining, sorting, and selecting the data. Most of the time, this work happens effectively without the database administrator having to be aware of what is going on, but occasionally, if the statistics no longer reflect what is actually in the table, then queries can suddenly run grindingly slow. At this point, the DBA must intervene to correct the problem.
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