Improperly sampled database statistics can cause SQL Server to generate inefficient query plans, resulting in poor performance for a particular query or group of queries. The following recommendations will help ensure that the database statistics will be properly sampled:
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Sample at 100% for all statistics in the database to obtain an accurate representation of the distribution of data in the system.
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Statistics should be updated on a weekly, bi-weekly, or monthly basis to ensure they that reflect the current set of data.
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Column statistics can be updated using the Update Statistics Task. If you plan to update index statistics via the Update Statistics Task within SQL Server, it is recommended that you select the All existing statistics option so that both index and column statistics are updated. If you rely on the Rebuild Index Task to update index statistics (see below), it is recommended that you create a separate Update Statistics Task which updates Column statistics only.