However, for some tables, such as those subject to significant changes in distribution, or those with skewed values, it’s possible that SQL Server’s automatic statistics update will be inadequate to maintain consistently high levels of query performance.
In this article, I’ll describe, briefly, when SQL Server creates statistics and its criteria for performing automatic statistics updates.
SQL Server will update each invalidated object, automatically, the next time the query optimizer needs to use that statistic.
The statistics are stored in system tables in the database.
In a multi-column statistic, whether index or column-level, the histogram only exists for the first column (they are “left-based”).
Integrity checks are also essential as database corruption must be found and corrected as quickly as possible, to mitigate downtime and data loss.
Finally, a DBA has to ensure that performance is optimal, and ensuring that statistics remain up-to-date and accurate is an important part of this task.
For example, if the index is on ( is not the leading column in another existing index).
After working with clients for several years, I realized there was some confusion surrounding indexes and statistics, particularly among “accidental” DBAs, or those that were new to database administration.
Note that since an index rebuild operation recreates the index, SQL Server will also update the index Statistics object.
Second, assuming the database option is enabled, which it is by default, SQL Server will create single-column statistics whenever a column, which is not already the leading column in an existing index, is used in a query predicate (e.g.
The optimizer obtains its knowledge of the data, its distribution, and the number of rows a given query is likely to return from the available statistics.