Updating statistics sql server does sarah harding present dating in the dark

The density vector contains one density for each prefix of columns in the statistics object.Note Frequency is information about the occurrence of each distinct value in the first key column of the statistics object, and is calculated as row count * density.In more detail, SQL Server creates the histogram from the sorted set of column values in three steps: Density is information about the number of duplicates in a given column or combination of columns and it is calculated as 1/(number of distinct values).The query optimizer uses densities to enhance cardinality estimates for queries that return multiple columns from the same table or indexed view.Before executing a cached query plan, the Database Engine verifies that the query plan references up-to-date statistics.

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.It applies strictly to single-column statistics for the full table.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update statistics option, AUTO_UPDATE_STATISTICS is ON, the Query Optimizer determines when statistics might be out-of-date and then updates them when they are used by a query.The range includes all possible column values between boundary values, excluding the boundary values themselves.The lowest of the sorted column values is the upper boundary value for the first histogram step.

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