OPENQUERY(linked_server,'query') 其中linked_server参数为连接的名称。而query参数为要进行的查询,它将以一个字符串的形式传送给OPENQUERY函数。此函数返回的将是一个虚拟表,从而可以让我们对其做进一步的查询。 下面的语句查找内容包含中SQL这个单词的所有文件: SELECT* FROMOpenQuery(FileSystem, 'SELECT Directory, ...
(*) AS COUNT FROM Sales.SalesOrderDetail AS od, Sales.SalesOrderHeader AS o WHERE od.SalesOrderID = o.SalesOrderID GROUP BY OrderDate, ProductID; GO -- Create an index on the view CREATE UNIQUE CLUSTERED INDEX IDX_V1 ON Sales.vOrders (OrderDate, ProductID); GO -- This query can ...
To see which indexes the query optimizer uses for a specific query, in SQL Server Management Studio, on the Query menu, select Include Actual Execution Plan.Don't always equate index usage with good performance, and good performance with efficient index use. If using an index always help...
(*) AS COUNT FROM Sales.SalesOrderDetail AS od, Sales.SalesOrderHeader AS o WHERE od.SalesOrderID = o.SalesOrderID GROUP BY OrderDate, ProductID; GO -- Create an index on the view CREATE UNIQUE CLUSTERED INDEX IDX_V1 ON Sales.vOrders (OrderDate, ProductID); GO -- This query can ...
OPENQUERY(linked_server, query) 其中linked_server参数为连接的名称。而query参数为要进行的查询,它将以一个字符串的形式传送给OPENQUERY函数。此函数返回的将是一个虚拟表,从而可以让我们对其做进一步的查询。 下面的语句查找内容包含中SQL这个单词的所有文件: SELECT * FROM OpenQuery(FileSystem, SELECT Directory,...
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SQL Server parse and compile time: CPU time = 0 ms, elapsed time = 0 ms. 在上述查询中,之所以要使用with (index (SalesOrderDetail_test_NCL_Price))这个语句,是为了强制其使用SalesOrderDetail_test_NCL_Price这个非聚集索引,通过非聚集索引找到了聚集索引键值以后再去聚集索引中查询。如果不使用的话,sql ...
When you run a parallel query in Microsoft SQL Server 2012, you may receive incorrect results. This problem occurs if the following conditions are true: The query runs against a partitioned table that has a columnstore index. The query uses an aggregate function over the columnstor...
When you run a parallel query in Microsoft SQL Server 2012, you may receive incorrect results. This problem occurs if the following conditions are true: The query runs against a partitioned table that has a columnstore index. The query uses an aggregate function over the columnstor...
SQL有一个查询优化分析器 Query Optimizer,其在执行查询之前首先会进行分析,当查询中有可以利用的索引时,那么就优先分析使用Index Seek进行查询的效率,假如得出使用Index Seek的查询效率并不好,那么就使用Index Scan进行查询。那究竟是在什么情况下会造成Index Seek效率比Index Scan还低呢?可以分一下集中情况: ...