How do I use cascade delete with SQL Server?

Question

I have 2 tables: T1 and T2, they are existing tables with data. We have a one to many relationship between T1 and T2. How do I alter the table definitions to perform casca

Answer 1

First To Enable ONCascade property:

1.Drop the existing foreign key constraint

2.add a new one with the ON DELETE CASCADE setting enabled

Ex:

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

Second To Disable ONCascade property:

1.Drop the existing foreign key constraint

2.Add a new one with the ON DELETE NO ACTION setting enabled

Ex:

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