删除数据

　　我们有两种方式删除数据，DELETE语句和TRUNCATE语句。需要注意它们的区别，DELETE语句是以完整模式记录日志的，所以它的性能相对较低。而TRUNCATE语句是以最小模式来记录日志的，并且它会重置标识种子。下面是示例代码。

USE tempdb;GO-- 准备测试数据IF OBJECT_ID('dbo.Orders','U') IS NOT NULL DROP TABLE dbo.Orders;IF OBJECT_ID('dbo.Customers','U') IS NOT NULL DROP TABLE dbo.Customers;GOSELECT * INTO dbo.Orders FROM TSQLFundamentals2008.Sales.Orders;SELECT * INTO dbo.Customers FROM TSQLFundamentals2008.Sales.Customers;ALTER TABLE dbo.Customers ADDCONSTRAINT PK_Customers PRIMARY KEY(custid);ALTER TABLE dbo.Orders ADDCONSTRAINT PK_Orders PRIMARY KEY(orderid),CONSTRAINT FK_Orders_Customers FOREIGN KEY(custid) REFERENCES dbo.Customers(custid);-- 删除数据-- 方法一：DELETE(完整模式日志,性能低)DELETE FROM dbo.OrdersWHERE orderdate<'20070101';-- 基于联接的DELETEDELETE FROM orders FROM dbo.Orders AS ordersLEFT JOIN dbo.Customers AS customers ON orders.custid= customers.custidWHERE customers.country= N'USA';-- 方法三：TRUNCATE(最小模式日志,性能高；重置标识种子)TRUNCATE TABLE dbo.Orders;