查询优化器不使用此 Density 值,显示此值的目的是为了与SQL Server 2008之前的版本实现向后兼容 Calculated as 1 / distinct values for all values in the first key column of the statistics object, excluding the histogram boundary values. This Density value is not used by the query optimizer and is ...
查询优化器不使用此 Density 值,显示此值的目的是为了与SQL Server 2008之前的版本实现向后兼容 Calculated as 1 / distinct values for all values in the first key column of the statistics object, excluding the histogram boundary values. This Density value is not used by the query optimizer and is ...
Run the Transact-SQL to ensure that your SQL Server database is set to the highest available compatibility level. Ensure that your database has its LEGACY_CARDINALITY_ESTIMATION configuration turned OFF. Clear your Query Store. In your database, ensure that Query Store is ON. Run the statement...
At a very high level, the CE process in SQL Server 2012 was the same through all prior releases back to SQL Server 7.0 (the release before SQL 2000). In recent years we tried to put a lot of fixes or QFEs in regards to query optimization (including cardinality estimation) ...
Cardinality estimation (CE) in SQL Server is derived primarily from histograms that are created when indexes or statistics are created, either manually or automatically. Sometimes, SQL Server also uses constraint information and logical rewrites of queries to determine cardinality....
The first factor, cardinality, is used as an input parameter of the second factor, the cost model. Therefore, improved cardinality leads to better estimated costs and, in turn, faster execution plans. Cardinality estimation (CE) in SQL Server is derived primarily from histograms that are creat...
A few of those assumptions changed in SQL Server 2014 CE, namely: Independence becomesCorrelation: The combination of the different column values are not necessarily independent. This may resemble more real-life data querying. Simple Containment becomesBase Containment: Users might ...
If you create a new database on SQL Server 2014, compatibility level will be 120. When you upgrade or restore from a previous version to SQL 2014, a user database compatibility level will not be updated. In other words, you will continue to use old cardinality estimator in upgrade and ...
Assume that you have enabledthe new cardinality estimatorin Microsoft SQL Server 2014. When you run a query that contains join statements, you may encounter the following issues: Some queries take significantly longer time to compile, especial...
Published: April 2014 Applies to: SQL Server 2014 To review the document, please download the Optimizing Your Query Plans with the SQL Server 2014 Cardinality Estimator Word document. Ask a question in the SQL Server Forums Send FeedbackEnglish...