Ms sql updating statistics

12-Sep-2016 07:39

Try as I might, I find it hard to over-emphasize the importance of statistics to SQL Server.Bad or missing statistics leads to poor choices by the optimizer: The result is horrific performance.They’re created at different points and, unless you’re creating the statistics manually yourself, they’re created slightly differently.

By default, SQL Server automatically creates statistics every time an unindexed column is referenced in a query’s WHERE or ON clause.

SQL Server Query Optimizer uses statistics to estimate the distribution of values in one or more columns of a table or index views, and the number of rows (called ) to create a high-quality query execution plan.

Often statistics are created on a single column but it’s not uncommon to create statistics on multiple columns.

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.

Based on this knowledge, it decides the optimal access path, making choices such as whether to scan a table or perform an index seek, use a nested loop join or a hash join, and so on.

By default, SQL Server automatically creates statistics every time an unindexed column is referenced in a query’s WHERE or ON clause.

SQL Server Query Optimizer uses statistics to estimate the distribution of values in one or more columns of a table or index views, and the number of rows (called ) to create a high-quality query execution plan.

Often statistics are created on a single column but it’s not uncommon to create statistics on multiple columns.

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.

Based on this knowledge, it decides the optimal access path, making choices such as whether to scan a table or perform an index seek, use a nested loop join or a hash join, and so on.

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.