Statistics maintenance

As mentioned previously, the Query Optimizer will, by default, automatically update statistics when they are out of date. Statistics can also be updated with the UPDATE STATISTICS statement, which you can schedule to run as a maintenance job. Another statement that’s commonly used, sp_updatestats, also runs UPDATE STATISTICS behind the scenes.

There are two important benefits of updating statistics in a maintenance job. The first is that your queries will use updated statistics without having to wait for the statistics to be automatically updated, thus avoiding delays in the optimization of your queries (although asynchronous statistics updates can also be used to partially help with this problem). The second benefit is that you can use a bigger sample than the Query Optimizer will use, or you can even scan the entire table. This can give you better-quality statistics for big tables, especially for those where data is not randomly distributed in their...