Rewriting updating maintenance procedures

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The Query Optimizer uses these statistics to estimate the enable the Query Optimizer to create a high-quality query plan.For example, depending on your predicates, the Query Optimizer could use cardinality estimates to choose the index seek operator instead of the more resource-intensive index scan operator, and in doing so improve query performance.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.For more information about the filter predicate, see CREATE STATISTICS (Transact-SQL).For more information about when to create filtered statistics, see the When to Create Statistics section in this topic.

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update statistics option, AUTO_UPDATE_STATISTICS is ON, the Query Optimizer determines when statistics might be out-of-date and then updates them when they are used by a query.There are three options that you can set that affect when and how statistics are created and updated.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.These single-column statistics are created on columns that do not already have a histogram in an existing statistics object.To create the histogram, the query optimizer sorts the column values, computes the number of values that match each distinct column value and then aggregates the column values into a maximum of 200 contiguous histogram steps.Each histogram step includes a range of column values followed by an upper bound column value.

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