When the SQL Server optimizer evaluates a query to determine how best to execute it, the statistics are quite possibly the most important tool at its disposal. But SQL Server statistics objects aren’t perfect because they only contain estimated summary information. In this session, we’ll start with an overview of what the statistics objects are, how the optimizer uses them, and some general guidelines for their maintenance. Then we’ll look at some of the issues, how to find them, and how to solve them, that can arise due to their imperfection: ascending keys (the most prevalent statistics based performance killer?), correlated predicates, skewed distribution, or downright bad summary information. There’ll be many examples, and even a stored procedure to help you find ascending keys. By applying the techniques we’ll discuss, you WILL see improved query performance.
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