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  SQL Server Tips by Gama and Naughter

 

Set NULL

 

The Set NULL action is implemented by triggers that will examine the data and then set to NULL the rows from table [Tbl B] related to changed or deleted records from table [Tbl A].

 

Delete Set NULL

 

Delete set NULL requires one trigger for table [Tbl A] that will set to NULL all the values of the related columns from table [Tbl B].

 

CREATE TRIGGER "[Tbl A DNTrig]" ON [Tbl A] FOR DELETE AS

SET NOCOUNT ON

/* * DELETE SET NULL TO '[Tbl B]' */

IF (SELECT COUNT(*) FROM deleted, [Tbl B] WHERE (deleted. [Col A]= [Tbl B]. [Col B])) > 0

       UPDATE [Tbl B]

       SET [Tbl B]. [Col B]=NULL

       FROM [Tbl B], deleted

       WHERE deleted. [Col A]= [Tbl B].[Col B]

 

Let us test the trigger:

 

DELETE [Tbl A] WHERE [col A]='value2'
 


The above book excerpt is from:

Super SQL Server Systems
Turbocharge Database Performance with C++ External Procedures

ISBN: 0-9761573-2-2
Joseph Gama, P. J. Naughter

 http://www.rampant-books.com/book_2005_2_sql_server_external_procedures.htm
 

 

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