Sorry leave both on. Create and Update.
As for the second question this is from BOL
When set to ON, statistics are automatically created on columns used in a predicate. Adding statistics improves query performance because the SQL Server query optimizer can better determine how to evaluate a query. If the statistics are not used, SQL Server automatically deletes them. When set to OFF, statistics are not automatically created by SQL Server; instead, statistics can be manually created. For more information, see Statistical Information.
By default, AUTO_CREATE_STATISTICS is ON.
The status of this option can be determined by examining the IsAutoCreateStatistics property of the DATABASEPROPERTYEX function.
When set to ON, existing statistics are automatically updated when the statistics become out-of-date because the data in the tables has changed. When set to OFF, existing statistics are not automatically updated; instead, statistics can be manually updated. For more information, see Statistical Information.
By default, AUTO_UPDATE_STATISTICS is set to ON.
The status of this option can be determined by examining the IsAutoUpdateStatistics property of the DATABASEPROPERTYEX function.
Create basically decides if a field is used for accessing the data in a where clause then build a stats value for it. Update keeps it current with the nature of ever changing data. These statistics are especially usefull when it comes to indexes in that the higher the statistics value the higher the uniqeuness of the column the more likely the index will be used. Without these stats query plans do not develope for these columns sometimes the way it is expected and when stats are out of date a field that may have the best possiblities for uniqueness (this means fewer records fit the profile) may not get used.
Hoep I got all that right and makes sense.
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