Sql commands for updating table
Creating statistics can take a few seconds on a single column depending on the size of the table.
To avoid measuring performance degradation, especially in performance benchmarking, you should ensure stats have been created first by executing the benchmark workload before profiling the system.
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The following guiding principles are provided for updating your statistics during the load process: For more information, see Cardinality Estimation.
These examples show how to use various options for creating statistics.
Conversely, statistics on a gender column in a customer table might never need to be updated.
However, if your data warehouse contains only one gender and a new requirement results in multiple genders, then you need to update statistics on the gender column.
However, if your data warehouse only contains one country and you bring in data from a new country, resulting in data from multiple countries being stored, then you need to update statistics on the country column.
The following are recommendations updating statistics: | Frequency of stats updates | Conservative: Daily After loading or transforming your data | | Sampling | Less than 1 billion rows, use default sampling (20 percent) With more than 1 billion rows, statistics on a 2-percent range is good | One of the first questions to ask when you're troubleshooting a query is, "Are the statistics up to date?
When the automatic create statistics option is on, AUTO_CREATE_STATISTICS, SQL Data Warehouse analyzes incoming user queries where single column statistics are created for columns which are missing statistics.
The query optimizer creates statistics on individual columns in the query predicate or join condition to improve cardinality estimates for the query plan.
For more information, see general guidance for Statistics.