Look at an example of a subquery, which is a query that is nested in a SELECT, INSERT, UPDATE, or DELETE statement, or inside another subquery in SQL Server.
以子查询A NOT IN S为例 等价变换为A <> ALL S 再次等价变换为NOT EXISTS子查询,即,NOT EXISTS(σ[A = s OR A IS NULL OR s IS NULL] S) 再次等价变换为含有OR的antijoin,利用antijoin的优化规则进一步优化 4. REMOVING APPLY 在SQL Server的优化器处理流程: query text - > operator tree RBO,对...
将SQL query的抽象语法树(AST)转换为SQL算子(operator)树。对于子查询来说,就是将子查询转换为Apply 算子。Apply算子是SQL Server一个算子,APPLY的左表达式:左表达式的每一行都和右表达式进行一次计算,即右表达式需要根据左表达式提供的值进行相关计算来获取相关结果,然后返回给客户端。APPLY的右表达式:是一个子查询或...
public boolean supportsSubqueriesInExists() 返回值true if supported. Otherwise, false.异常SQLServerException备注This supportsSubqueriesInExists method is specified by the supportsSubqueriesInExists method in the java.sql.DatabaseMetaData interface.另
SQL WHEREEXISTS(sub query) Suppose we need to return all sales orders written by sales people with sales year to date greater than three million dollars. To do so, we can use theEXISTSclause as shown in this example: SQL SELECTSalesOrderID, ...
Microsoft JDBC Driver для SQL Server Началоработы Обзор Справочникпо API Справочникпо API Интерфейс ISQLServerCallableStatement Интерфейс ISQLServerConnection Интерфейс ISQLServerDataSource Ин...
SQL Server won't have to return data about the related orders for customers who have placed orders. If a custid is found in the Sales.SalesOrderHeader table, NOT EXISTS evaluates to FALSE and the evaluation quickly completes.To write queries that use EXISTS with subqueries, consider the ...
Another use of the INSERT...SELECT statement is to insert data from a source outside SQL Server. The SELECT in the INSERT statement can be used for the following: Reference a remote table on a linked server by using a four-part name. For more information,Identifying a Data Source by Usi...
Another use of the INSERT...SELECT statement is to insert data from a source outside SQL Server. The SELECT in the INSERT statement can be used for the following: Reference a remote table on a linked server by using a four-part name. For more information,Identifying a Data Source by Usi...
Microsoft SQL Server.Optimizing SQL subqueries has been an active area in database research and the database industry throughout the last decades. Previous work has already identified some approaches to efficiently execute relational subqueries. For satisfactory performance, proper choice of subquery ...