But before I move to optimize those, I would like to point out a very simple change in my query that will allow me to eliminate two of the operators altogether.Figure 3 Total estimated execution cost of the querySince the only column I am returning from the Sales.Customer table is ...
SQL Server OPTION (OPTIMIZE FOR UNKNOWN) 测试总结 关于SQL Server的查询提示OPTION (OPTIMIZE FOR UNKNOWN),它是解决参数嗅探的方法之一。 而且对应的SQL语句会缓存,不用每次都重编译。关键在于它的执行计划的准确度问题, 最近在优化的时候,和同事对于这个查询提示(Query Hint)有一点分歧,遂动手实验验证、总结了一...
提示 另一个选项是使用OPTIMIZE FOR查询提示。这告诉SQL Server在编译计划时使用指定的值。如果通过测试,你可以找到一个值,每次产生一个“足够好”的计划,而性能不大不小可以接受,这是一个很好的选择。 ALTERPROCEDUREGet_OrderID_OrderQty@ProductIDINTASSELECTSalesOrderDetailID, OrderQtyFROMSales.SalesOrderDetailWHER...
For example, we could create another query from another application that has the same structure (does the same thing) and SQL Server and query optimizer will use this execution plan again because it is parameterized which means that the query plan is really the same it’s just the value that...
OPTIMIZE FOR ( @variable_name { UNKNOWN | = <literal_constant> } [ , ...n ] ) Instructs the Query Optimizer to use a particular value for a local variable when the query is compiled and optimized. The value is used only during query optimization, and not during query execution. @vari...
Like interpreted stored procedures, natively compiled stored procedures also support the OPTIMIZE FOR hint. For more information, see Query Hints (Transact-SQL). Retrieving a Query Execution Plan for Natively Compiled Stored Procedures The query execution plan for a natively compile...
1. OPTIMIZE FOR Unknown SQL Server 2005版本中增加了OPTIMIZE FOR提示(hint),允许DBA确定用于基数评估和优化的字面值。如果我们有一张数据分布倾斜的表,OPTIMIZE FOR能被用于优化为广泛范围参数值提供合理性能的通用值。当对所有参数值来说性能并非最好时,相比有时做查找(seek,对于选择性较好的参数值),有时做扫描...
NoteSQL Server requires certain conditions to be met in order to allow the use of calculated fields and indexed views (set quoted_identifier on,set arithabort on, and so on). Indexed views are a good way to further speed up the query if you are not satisfied with the results. Indexed vi...
使用OPTIMIZE FOR 提示为特定参数值生成执行计划 使用查询存储的最后一个已知良好计划 下面提到的所有方法都需要人工干预,要么在 SQL 代码级别添加查询提示,要么由 DBA 强制执行特定的执行计划。 新功能:PSP优化 这一新的 PSP 优化功能将在 SQL Server 2022 中引入,并在兼容级别 160 时默认启用。
SQL Server Statistics and Cost Estimation 统计信息(Statistics)会干扰查询优化器(Query Optimizer)生成最优的执行计划。它存储的是表列或者索引列的数值分布统计,也称为柱状统计Histogram。统计信息的过期或者不充分,都能导致优化器评估成本模型(Cost-Based Estimation)失效。所以我们就要时刻监控统计信息的有效性,采取适...