Blogger Jeff = new Blogger

Programming and stuff in Western PA

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:

About these ads

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

1 Comment »

  1. What about when you have two referential columns in the same table (e.g. ‘icon’ and ‘background’ both refer to the ‘image’ table)?

    In this example, SQL Server doesn’t allow both columns to have on-delete actions and I have to go back to stored procedures.

    It’s a ridiculous mess, and a bit shameful since it is 2010 and other databases have provided this functionality for years.

    Comment by Mike | April 12, 2010 | Reply


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Follow

Get every new post delivered to your Inbox.

%d bloggers like this: