Question

Hello friends I am getting the following error while making the foreign key

‘tbl_course’ table saved successfully
‘tbl_students’ table
– Unable to create relationship ‘FK_tbl_students_tbl_course’.
Introducing FOREIGN KEY constraint
‘FK_tbl_students_tbl_course’ on table
‘tbl_students’ may cause cycles or
multiple cascade paths. Specify ON
DELETE NO ACTION or ON UPDATE NO
ACTION, or modify other FOREIGN KEY
constraints. Could not create
constraint. See previous errors.

I have the following tables College table, Branch table, Course table and Student table

Course has a foreign key college_id, Branch has a foreign key course_id and I want to make college_id, course_id, branch_id as foreign keys to my Student table but while making course_id and branch_id as foreign key in Student table it generate the error mentioned above…please help me to resolve the above problem…..thanks

Answer 1

According to MS

You receive this error message because in SQL Server, a table cannot appear more than one time in a list of all the cascading referential actions that are started by either a DELETE or an UPDATE statement. For example, the tree of cascading referential actions must only have one path to a particular table on the cascading referential actions tree.

http://support.microsoft.com/kb/321843

Can you live without the cascading deletes? Keep the referential ingegrity but not the referenctial actions (cascades). You could resort to a trigger as a work around if needed.

EDIT:

CREATE TRIGGER [dbo].[tr_College_Delete] ON [dbo].[College] 
FOR  DELETE 
AS 
BEGIN 
    DELETE  FROM student 
    where collegeid in (select collegeid from deleted) 

END 

not tested.