Wednesday, 29 October 2008

SQL Server Cascade Delete

Just came across one of the most useful scripts ever! It can be a real pain in the arse when you need to delete some data from a table , then find out that some data somewhere else depends upon what you want to delete, and some data somewhere else relies on that, and so on and so on.

Well this script from Tim Young, creates a stored procedure that does everything for you. You just pass it the name of your table and some criteria (like user='bob') and it will delete all the referencing data and also print out the DELETE statements it created.

See the link below for a full example and explanation

But if you can't wait and just want to see the store procedure, here you go

P.S. I got this to work on SQLServer 2005.

Here’s the code for the procedure:

CREATE Procedure spDeleteRows
Recursive row delete procedure.

It deletes all rows in the table specified that conform to the criteria selected,
while also deleting any child/grandchild records and so on. This is designed to do the
same sort of thing as Access's cascade delete function. It first reads the sysforeignkeys
table to find any child tables, then deletes the soon-to-be orphan records from them using
recursive calls to this procedure. Once all child records are gone, the rows are deleted
from the selected table. It is designed at this time to be run at the command line. It could
also be used in code, but the printed output will not be available.

@cTableName varchar(50), /* name of the table where rows are to be deleted */
@cCriteria nvarchar(1000), /* criteria used to delete the rows required */
@iRowsAffected int OUTPUT /* number of records affected by the delete */
set nocount on
declare @cTab varchar(255), /* name of the child table */
@cCol varchar(255), /* name of the linking field on the child table */
@cRefTab varchar(255), /* name of the parent table */
@cRefCol varchar(255), /* name of the linking field in the parent table */
@cFKName varchar(255), /* name of the foreign key */
@cSQL nvarchar(1000), /* query string passed to the sp_ExecuteSQL procedure */
@cChildCriteria nvarchar(1000), /* criteria to be used to delete
records from the child table */

@iChildRows int /* number of rows deleted from the child table */

/* declare the cursor containing the foreign key constraint information */
SELECT AS Tab, AS Col, AS RefTab, AS RefCol, AS FKName
FROM dbo.sysforeignkeys FK
INNER JOIN dbo.syscolumns SC1 ON FK.fkeyid =
AND FK.fkey = SC1.colid
INNER JOIN dbo.syscolumns SC2 ON FK.rkeyid =
AND FK.rkey = SC2.colid
INNER JOIN dbo.sysobjects SO1 ON FK.fkeyid =
INNER JOIN dbo.sysobjects SO2 ON FK.rkeyid =
INNER JOIN dbo.sysobjects FO ON FK.constid =
WHERE SO2.Name = @cTableName

FETCH NEXT FROM cFKey INTO @cTab, @cCol, @cRefTab, @cRefCol, @cFKName
/* build the criteria to delete rows from the child table. As it uses the
criteria passed to this procedure, it gets progressively larger with
recursive calls */

SET @cChildCriteria = @cCol + ' in (SELECT [' + @cRefCol + '] FROM [' +
@cRefTab +'] WHERE ' + @cCriteria + ')'
print 'Deleting records from table ' + @cTab
/* call this procedure to delete the child rows */
EXEC spDeleteRows @cTab, @cChildCriteria, @iChildRows OUTPUT
FETCH NEXT FROM cFKey INTO @cTab, @cCol, @cRefTab, @cRefCol, @cFKName
Close cFKey
DeAllocate cFKey
/* finally delete the rows from this table and display the rows affected */
SET @cSQL = 'DELETE FROM [' + @cTableName + '] WHERE ' + @cCriteria
print @cSQL
EXEC sp_ExecuteSQL @cSQL
print 'Deleted ' + CONVERT(varchar, @@ROWCOUNT) + ' records from table ' + @cTableName

In the above scenario, we were trying to perform the following :

    DELETE FROM X WHERE field1 = '234'

Using this procedure, we would use the following command:

    exec spDeleteRows 'X', 'field1 = ''234''', 0