如何在SQL Server中使用级联删除？

Question

我有2个表:T1和T2,它们是带有数据的现有表.我们在T1和T2之间有一对多的关系.当删除T1中的记录时,如何更改表定义以在SQL Server中执行级联删除,T2中的所有关联记录也将被删除.

他们之间存在外来约束.我不想删除表或创建触发器来删除T2.例如,当我删除员工时,所有审核记录也应该消失.

T1 - 员工,

Employee ID      
Name
Status

T2 - 性能评测,

Employee ID - 2009 Review
Employee ID - 2010 Review

Answer 1

你需要,

• 删除现有的外键约束,
• 在ON DELETE CASCADE启用设置的情况下添加新的.

就像是:

ALTER TABLE dbo.T2
   DROP CONSTRAINT FK_T1_T2   -- or whatever it's called

ALTER TABLE dbo.T2
   ADD CONSTRAINT FK_T1_T2_Cascade
   FOREIGN KEY (EmployeeID) REFERENCES dbo.T1(EmployeeID) ON DELETE CASCADE

Answer 2

要将"级联删除"添加到SQL Server Management Studio中的现有外键:

首先,选择您的外键,并在新的查询窗口中打开它的"DROP和Create To ..".

然后,只需添加ON DELETE CASCADE到ADD CONSTRAINT命令:

然后点击"执行"按钮运行此查询.

顺便说一句,要获取外键列表,并查看哪些已打开"级联删除",您可以运行此脚本:

SELECT 
   OBJECT_NAME(f.parent_object_id) AS 'Table name',
   COL_NAME(fc.parent_object_id,fc.parent_column_id) AS 'Field name',
   delete_referential_action_desc AS 'On Delete'
FROM sys.foreign_keys AS f,
     sys.foreign_key_columns AS fc,
     sys.tables t 
WHERE f.OBJECT_ID = fc.constraint_object_id
AND t.OBJECT_ID = fc.referenced_object_id
ORDER BY 1

如果您DROP因为外键约束而发现您不能使用特定的表,但是您无法确定哪个FK导致了问题,那么您可以运行以下命令:

sp_help 'TableName'

该文章中的SQL列出了引用特定表的所有FK.

希望这一切都有帮助.

道歉为长指.我只是想说明一点.

Answer 3

您可以使用SQL Server Management Studio执行此操作.

→右键单击表格设计并转到"关系"并选择左侧窗格和右侧窗格中的外键,展开"INSERT和UPDATE规范"菜单,然后选择"级联"作为删除规则.

Answer 4

使用类似的东西

ALTER TABLE T2
ADD CONSTRAINT fk_employee
FOREIGN KEY (employeeID)
REFERENCES T1 (employeeID)
ON DELETE CASCADE;

填写正确的列名称,您应该设置.正如mark_s正确陈述的那样,如果您已经有外键约束,则可能需要先删除旧的约束,然后再创建新的约束.

Answer 5

ON DELETE CASCADE
它指定删除父数据时删除子数据.

CREATE TABLE products
( product_id INT PRIMARY KEY,
  product_name VARCHAR(50) NOT NULL,
  category VARCHAR(25)
);

CREATE TABLE inventory
( inventory_id INT PRIMARY KEY,
  product_id INT NOT NULL,
  quantity INT,
  min_level INT,
  max_level INT,
  CONSTRAINT fk_inv_product_id
    FOREIGN KEY (product_id)
    REFERENCES products (product_id)
    ON DELETE CASCADE
);

对于这个外键,我们指定了一个ON DELETE CASCADE子句,它告诉SQL Server删除父表中的数据时删除子表中的相应记录.因此,在此示例中,如果从products表中删除product_id值,则还将删除使用此product_id的库存表中的相应记录.

Answer 6

首先启用ONCascade属性:

1.Drop现有的外键约束

2.在启用ON DELETE CASCADE设置的情况下添加新的

例如:

IF EXISTS(SELECT 1 FROM sys.foreign_keys WHERE parent_object_id = OBJECT_ID(N'dbo.Response'))
 BEGIN 

ALTER TABLE [dbo].[Response] DROP CONSTRAINT [FK_Response_Request]  

ALTER TABLE [dbo].[Response] WITH CHECK ADD CONSTRAINT [FK_Response_Request]  FOREIGN KEY([RequestId])
REFERENCES [dbo].[Request] ([RequestId])
ON DELETE CASCADE
END

ELSE

 BEGIN 
 ALTER TABLE [dbo].[Response] WITH CHECK ADD CONSTRAINT [FK_Response_Request]  FOREIGN KEY([RequestId])
REFERENCES [dbo].[Request] ([RequestId])
ON DELETE CASCADE
END

第二个禁用ONCascade属性:

1.Drop现有的外键约束

2.在启用ON DELETE NO ACTION设置的情况下添加新的设置

例如:

IF EXISTS(SELECT 1 FROM sys.foreign_keys WHERE parent_object_id = OBJECT_ID(N'dbo.Response'))
 BEGIN 
ALTER TABLE [dbo].[Response] DROP CONSTRAINT [FK_Response_Request]  

ALTER TABLE [dbo].[Response] WITH CHECK ADD CONSTRAINT [FK_Response_Request]  FOREIGN KEY([RequestId])
REFERENCES [dbo].[Request] ([RequestId])
ON DELETE CASCADE
END

ELSE

 BEGIN 
 ALTER TABLE [dbo].[Response] WITH CHECK ADD CONSTRAINT [FK_Response_Request]  FOREIGN KEY([RequestId])
REFERENCES [dbo].[Request] ([RequestId])
ON DELETE NO ACTION 
END