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Cascading deletes in SQL Server

I get asked from time to time if SQL Server supports cascading deletes, and the answer is Yes. SQL Server does so via foreign key constraints with the DELETE CASCADE flag set. In the following example, after creating the objects and inserting some data, we delete a USR_ID from the parent data. After querying the child table (USER_PHONE) a second time, we can see that the cascading delete worked :

CREATE TABLE USERS
(
    USR_ID int
    ,CONSTRAINT [PK_Temp_Users1] PRIMARY KEY CLUSTERED ([USR_ID])
)

CREATE TABLE USER_PHONE
(
    USR_ID int
    ,CONSTRAINT [PK_Temp_Users2] PRIMARY KEY CLUSTERED ([USR_ID])
)
ALTER TABLE [dbo].USER_PHONE  WITH CHECK ADD  
CONSTRAINT [FK_Temp_UsersPhone_Users] FOREIGN KEY([USR_ID])
REFERENCES [dbo].[Users] ([USR_ID])
ON DELETE CASCADE
GO

INSERT INTO USERS
    SELECT 1 UNION SELECT 2 UNION SELECT 3

INSERT INTO USER_PHONE
    SELECT 1 UNION SELECT 2 UNION SELECT 3

SELECT * FROM USER_PHONE
DELETE USERS WHERE USR_ID=2
SELECT * FROM USER_PHONE

DROP TABLE USER_PHONE
DROP TABLE USERS

Tags: SQL Server

January 28, 2008 - Posted by rudesyle | SQL Server, Technology