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Erschienen in:
2018 | OriginalPaper | Buchkapitel
13. Statistics, Data Distribution, and Cardinality
verfasst von : Grant Fritchey
Erschienen in: SQL Server 2017 Query Performance Tuning
Verlag: Apress
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Abstract
By now, you should have a good understanding of the importance of indexes. But, the index alone is not what the optimizer uses to determine how it’s going to access data. It also takes advantage of enforced referential constraint and other table structures. Finally, and possibly most important, the optimizer must have information about the data that defines an index or a column. That information is referred to as a statistic. Statistics define both the distribution of data and the uniqueness or selectivity of the data. Statistics are maintained both on indexes and on columns within the system. You can even define statistics manually yourself.