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  • 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;
    GO
    
    SELECT * INTO dbo.Orders FROM TSQLFundamentals2008.Sales.Orders;
    SELECT * INTO dbo.Customers FROM TSQLFundamentals2008.Sales.Customers;
    
    ALTER TABLE dbo.Customers ADD
    CONSTRAINT PK_Customers PRIMARY KEY(custid);
    
    ALTER TABLE dbo.Orders ADD
    CONSTRAINT 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.Orders
    WHERE orderdate<'20070101';
    
    -- 基于联接的DELETE
    DELETE FROM orders 
    FROM dbo.Orders AS orders
    LEFT JOIN dbo.Customers AS customers ON orders.custid= customers.custid
    WHERE 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;
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  • 原文地址:https://www.cnblogs.com/mcgrady/p/3978907.html
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