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The query optimizer uses densities to enhance cardinality estimates for queries that return multiple columns from the same table or indexed view.The density vector contains one density for each prefix of columns in the statistics object.For most queries, the Query Optimizer already generates the necessary statistics for a high quality query plan; in some cases, you need to create additional statistics or modify the query design for best results.
A histogram measures the frequency of occurrence for each distinct value in a data set.
The query optimizer computes a histogram on the column values in the first key column of the statistics object, selecting the column values by statistically sampling the rows or by performing a full scan of all rows in the table or view.
For more information about when to create filtered statistics, see the When to Create Statistics section in this topic.
There are three options that you can set that affect when and how statistics are created and updated. When the automatic create statistics option, AUTO_CREATE_STATISTICS is ON, the Query Optimizer creates statistics on individual columns in the query predicate, as necessary, to improve cardinality estimates for the query plan.
Each histogram step includes a range of column values followed by an upper bound column value.
The range includes all possible column values between boundary values, excluding the boundary values themselves.This option also does not generate filtered statistics.It applies strictly to single-column statistics for the full table.Statistics for query optimization are binary large objects (BLOBs) that contain statistical information about the distribution of values in one or more columns of a table or indexed view.The Query Optimizer uses these statistics to estimate the enable the Query Optimizer to create a high-quality query plan.When the Query Optimizer creates statistics as a result of using the AUTO_CREATE_STATISTICS option, the statistics name starts with SELECT OBJECT_NAME(s.object_id) AS object_name, COL_NAME(sc.object_id, sc.column_id) AS column_name, AS statistics_name FROM sys.stats AS s INNER JOIN sys.stats_columns AS sc ON s.stats_id = sc.stats_id AND s.object_id = sc.object_id WHERE like '_WA%' ORDER BY s.name; When the automatic update statistics option, AUTO_UPDATE_STATISTICS is ON, the Query Optimizer determines when statistics might be out-of-date and then updates them when they are used by a query.Tags: Adult Dating, affair dating, sex dating