UPDATE STATISTICS (Transact-SQL)

Article
05/16/2013

Updates query optimization statistics on a table or indexed view. By default, the query optimizer already updates statistics as necessary to improve the query plan; in some cases you can improve query performance by using UPDATE STATISTICS or the stored procedure sp_updatestats to update statistics more frequently than the default updates.

Updating statistics ensures that queries compile with up-to-date statistics. However, updating statistics causes queries to recompile. We recommend not updating statistics too frequently because there is a performance tradeoff between improving query plans and the time it takes to recompile queries. The specific tradeoffs depend on your application. UPDATE STATISTICS can use tempdb to sort the sample of rows for building statistics.

Topic link icon Transact-SQL Syntax Conventions

Syntax

UPDATE STATISTICS table_or_indexed_view_name 
    [ 
        { 
            { index_or_statistics__name }
          | ( { index_or_statistics_name } [ ,...n ] ) 
                }
    ] 
    [    WITH 
        [ 
            FULLSCAN 
            | SAMPLE number { PERCENT | ROWS } 
            | RESAMPLE 
            | <update_stats_stream_option> [ ,...n ]
        ] 
        [ [ , ] [ ALL | COLUMNS | INDEX ] 
        [ [ , ] NORECOMPUTE ] 
    ] ;

<update_stats_stream_option> ::=
    [ STATS_STREAM = stats_stream ]
    [ ROWCOUNT = numeric_constant ]
    [ PAGECOUNT = numeric_contant ]

Arguments

table_or_indexed_view_name
Is the name of the table or indexed view to update statistics on.
index_or_statistics_name
Is the name of the index to update statistics on or name of the statistics to update. If index_or_statistics_name is not specified, the query optimizer updates all statistics for the table or indexed view. This includes statistics created using the CREATE STATISTICS statement, single-column statistics created when AUTO_CREATE_STATISTICS is on, and statistics created for indexes.

For more information about AUTO_CREATE_STATISTICS, see ALTER DATABASE SET Options (Transact-SQL). To view all indexes for a table or view, you can use sp_helpindex.
FULLSCAN
Compute statistics by scanning all rows in the table or indexed view. FULLSCAN and SAMPLE 100 PERCENT have the same results. FULLSCAN cannot be used with the SAMPLE option.
SAMPLE number { PERCENT | ROWS }
Specifies the approximate percentage or number of rows in the table or indexed view for the query optimizer to use when it updates statistics. For PERCENT, number can be from 0 through 100 and for ROWS, number can be from 0 to the total number of rows. The actual percentage or number of rows the query optimizer samples might not match the percentage or number specified. For example, the query optimizer scans all rows on a data page.

SAMPLE is useful for special cases in which the query plan, based on default sampling, is not optimal. In most situations, it is not necessary to specify SAMPLE because the query optimizer uses sampling and determines the statistically significant sample size by default, as required to create high-quality query plans.

SAMPLE cannot be used with the FULLSCAN option. When neither SAMPLE nor FULLSCAN is specified, the query optimizer uses sampled data and computes the sample size by default.

We recommend against specifying 0 PERCENT or 0 ROWS. When 0 PERCENT or ROWS is specified, the statistics object is updated but does not contain statistics data.
RESAMPLE
Update each statistic using its most recent sample rate.

Using RESAMPLE can result in a full-table scan. For example, statistics for indexes use a full-table scan for their sample rate. When none of the sample options (SAMPLE, FULLSCAN, RESAMPLE) are specified, the query optimizer samples the data and computes the sample size by default.
ALL | COLUMNS | INDEX
Update all existing statistics, statistics created on one or more columns, or statistics created for indexes. If none of the options are specified, the UPDATE STATISTICS statement updates all statistics on the table or indexed view.
NORECOMPUTE
Disable the automatic statistics update option, AUTO_UPDATE_STATISTICS, for the specified statistics. If this option is specified, the query optimizer completes this statistics update and disables future updates.

To re-enable the AUTO_UPDATE_STATISTICS option behavior, run UPDATE STATISTICS again without the NORECOMPUTE option or run sp_autostats.

Warning

Using this option can produce suboptimal query plans. We recommend using this option sparingly, and then only by a qualified system administrator.

For more information about the AUTO_STATISTICS_UPDATE option, see ALTER DATABASE SET Options (Transact-SQL).
<update_stats_stream_option>
Identified for informational purposes only. Not supported. Future compatibility is not guaranteed.

Remarks

When to Use UPDATE STATISTICS

For more information about when to use UPDATE STATISTICS, see Statistics.

Updating All Statistics with sp_updatestats

For information about how to update statistics for all user-defined and internal tables in the database, see the stored procedure sp_updatestats (Transact-SQL). For example, the following command calls sp_updatestats to update all statistics for the database.

EXEC sp_updatestats;

Determining the Last Statistics Update

To determine when statistics were last updated, use the STATS_DATE function.

Permissions

Requires ALTER permission on the table or view.

Examples

A. Update all statistics on a table

The following example updates the statistics for all indexes on the SalesOrderDetail table.

    USE AdventureWorks2012;
    GO
    UPDATE STATISTICS Sales.SalesOrderDetail;
    GO

B. Update the statistics for an index

The following example updates the statistics for the AK_SalesOrderDetail_rowguid index of the SalesOrderDetail table.

    USE AdventureWorks2012;
    GO
    UPDATE STATISTICS Sales.SalesOrderDetail AK_SalesOrderDetail_rowguid;
    GO

C. Update statistics by using 50 percent sampling

The following example creates and then updates the statistics for the Name and ProductNumber columns in the Product table.

    USE AdventureWorks2012;
    GO
    CREATE STATISTICS Products
        ON Production.Product ([Name], ProductNumber)
        WITH SAMPLE 50 PERCENT
    -- Time passes. The UPDATE STATISTICS statement is then executed.
    UPDATE STATISTICS Production.Product(Products) 
        WITH SAMPLE 50 PERCENT;

D. Update statistics by using FULLSCAN and NORECOMPUTE

The following example updates the Products statistics in the Product table, forces a full scan of all rows in the Product table, and turns off automatic statistics for the Products statistics.

    USE AdventureWorks2012;
    GO
    UPDATE STATISTICS Production.Product(Products)
        WITH FULLSCAN, NORECOMPUTE;
    GO

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