I have a table ParentTable (id, Name, town) and its child table human (mother, father) in which both columns contain mappings to the parent table.
The parent table has the column town which contain foreign key reference with Town (townid, townname) and that town is added with foreign key reference.
Now the problem is I need to give the cascade constraint for human table, but in SQL Server multiple column for the same parent table can not be given cascade. So I created trigger like this,
create trigger DEL_Parent
ON Parent
instead of delete as
set nocount on
delete from human
where mother IN (select id from deleted)
or father IN (select id from deleted)
delete from Parent where id in(select id from deleted).
But when I try to execute the trigger, the system shows the following error
Cannot create instead of delete or instead of update trigger
DEL_Parent on table Parent. This is because the table has a foreign
key with cascading delete or update.
How could resolve the problem? Thanks in advance.
Modify the query as:
create trigger DEL_Parent
ON Parent
after delete as
set nocount on
delete
from human
where mother IN (select id from deleted)
or father IN (select id from deleted)
delete
from Parent
where id in(select id from deleted)
because INSTEAD OF DELETE triggers cannot be defined on a table that has a foreign key defined with a DELETE action.
INSTEAD OF DELETE triggers cannot be defined on a table that has a foreign key defined with a DELETE action.
Source: http://msdn.microsoft.com/en-us/library/ms191208(v=sql.90).aspx
So, I guess if you wanted to you would have to drop your cascade delete and handle that with a trigger if you still wanted to enforce it.
Related
I have 2 tables, first one is Compartment and second one is AboveCompartment. Please see the below. Above compartment has 2 columns which are foreign keys and reference to the Compartment table. When I set the delete and update action as cascade for 2 foreign keys, I get the error below.
Introducing FOREIGN KEY constraint 'FK_AboveCompartment_Compartment1' on table 'AboveCompartment' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints.
Below CompId and AboveCompId are foreign keys and reference to the Compartment table. Which way should I follow to add delete cascading? I used the trigger below but it also didn't work and get error added below.
AboveCompartment
Compartment
Trigger
ALTER TRIGGER [dbo].[delFromCompartment] on [dbo].[Compartment]
FOR DELETE
AS
DELETE FROM dbo.AboveCompartment
WHERE CompId IN(SELECT deleted.Id FROM deleted)
Error
You cannot implement this using cascades, as SQL Server does not let you.
You also cannot implement it using triggers, because the foreign key is enforced before you get to the trigger.
You need to write a stored procedure that first deletes the parent table rows, then the child table
CREATE OR ALTER PROCEDURE dbo.Delete_Compartment
#CompartmentId int
AS
SET XACT_ABORT, NOCOUNT ON; -- always use XACT_ABORT if you have a transaction
BEGIN TRAN;
DELETE AboveCompartment
WHERE CompId = #CompartmentId;
DELETE AboveCompartment
WHERE AboveCompId = #CompartmentId;
DELETE Compartment
WHERE Id = #CompartmentId;
COMMIT;
I must say, this table design is somewhat suspect. AboveCompId as a column name implies that it represents a single parent for multiple children, rather than multiple parents for multiple children.
If so then you should instead implement this as a self-referencing foreign key. Drop the AboveCompartment table, and add a column
ALTER TABLE Compartment
ADD AboveCompId int NULL REFERENCES Compartment (Id);
This foreign key also cannot be cascading. But now the delete is only on one table, but you can do it in a recursive fashion. As long as you delete all rows in one go, you shouldn't have an issue with foreign key conflicts.
CREATE OR ALTER PROCEDURE dbo.Delete_Compartment
#CompartmentId int
AS
SET NOCOUNT ON;
-- no transaction needed as it's one statement
WITH cte AS (
SELECT #CompartmentId AS Id
UNION ALL
SELECT c.Id
FROM Compartment c
JOIN cte ON cte.Id = c.AboveCompId;
)
DELETE c
FROM Compartment c
JOIN cte ON cte.Id = c.Id;
I have a comment table that is self-referencing.
I tried to write on delete cascade but it take some exception
Introducing FOREIGN KEY constraint 'FK_Comments_Comments' on table 'Comments' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints.
and then try to write a trigger but it take exception again
CREATE TRIGGER [dbo].[T_comment_Trigger]
ON [dbo].[Comments]
FOR DELETE
AS
DELETE FROM Comments
WHERE ParentId =(SELECT deleted.id FROM deleted)
couldn't delete rows that have children
how can I do on delete cascade for my self-referencing table?
Assuming you're keeping your FOREIGN KEY constraint in place, you cannot fix the issue in a FOR DELETE trigger. FOR triggers (also known as AFTER triggers) fire after the activity has taken place. And a foreign key will prevent a row from being deleted if it has references. Foreign key checks occur before deletion.
What you need is an INSTEAD OF trigger. You also need to bear in mind that your current trigger only tried to deal with one "level" of referencing. (So, if row 3 references row 2 and row 2 references row 1, and you delete row 1, your trigger only tried to remove row 2)
So, something like:
CREATE TRIGGER [dbo].[T_comment_Trigger]
ON [dbo].[Comments]
INSTEAD OF DELETE
AS
;WITH IDs as (
select id from deleted
union all
select c.id
from Comments c
inner join
IDs i
on
c.ParentID = i.id
)
DELETE FROM Comments
WHERE id in (select id from IDs);
If there are other (non-self-referencing) cascading foreign key constraints, they all have to be replaced by actions in this trigger. In such a case, I'd recommend introducing a table variable to hold the list of all IDs that will eventually be deleted from the Comments table:
CREATE TRIGGER [dbo].[T_comment_Trigger]
ON [dbo].[Comments]
INSTEAD OF DELETE
AS
declare #deletions table (ID varchar(7) not null);
;WITH IDs as (
select id from deleted
union all
select c.id
from Comments c
inner join
IDs i
on
c.ParentID = i.id
)
insert into #deletions(ID)
select ID from IDs
-- Delete from FK referenced table
DELETE FROM OtherTable
WHERE CommentID in (select ID from #deletions)
--This delete comes last
DELETE FROM Comments
WHERE id in (select ID from #deletions);
I have the table with one primary key and one foreign key referencing the same table primary key.
i.e there are parents and childs in the same table. In sql sever there are three options for the delete rule. But it is only possible to set "NO ACTION" delete rule. I understand that it is not possible to set the "cascade" delete because of cycles and chaining. But why the other options are not allowed? Especially the "SET NULL" one.
Right now I have to do this manually. I have to find the child records and set the foreign key on null. After that I can delete the parent. Why is it not possible to set the rule for it?
Because it cannot perform two actions on the same table together which are:
-delete the parent.
-update the children.
A mutating table is a table that is being modified by an UPDATE, DELETE, or INSERT statement, or a table that might be updated by the effects of a DELETE CASCADE constraint.
you can overcome doing it manually by creating a procedure that would hold the parent key to delete the record and set the children to NULL.
procedure(parent_id) --takes the id as a parameter
update table set null where foreign_key = parent_id;
delete from table where id = parent_id;
end;
I have a problem with sql server, when I want to have 3 table and make relationship between them, and change the "On Update" property to "cascade".
this problem happend when I want to save the diagram:
Introducing FOREIGN KEY constraint 'FK_Company_Slave' on table 'Company' 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.
in this picture, I define my data base, FK and ....
thanks.
First:
A FOREIGN KEY in one table points to a PRIMARY KEY in another table. if you don't want to use PRIMARY KEY on other table in order to foreign key, you must be create unique index on the table.
Second:
you can create after trigger on Master table in order to develop on update cascade manually. In other word your foreign key between Company table and Master table created without on update cascade and then create following trigger on master to update company table after changed row in Master table.
create trigger triggername on dbo.[Master]
After Insert
AS Begin
Update Company
Set MasterKey = I.MasterKey
From Inserted I
Inner join Deleted D on D.Code = I.Code
Where Company.MasterKey = D.MasterKey
End
Create Trigger:
SELECT #oldVersionId = (SELECT DISTINCT VERSION_ID FROM Deleted)
SELECT #newVersionId = (SELECT DISTINCT VERSION_ID FROM Inserted)
SELECT #appId = (SELECT DISTINCT APP_ID FROM Deleted)
UPDATE [TableName]
SET [VERSION_ID] = #newVersionId
WHERE (([VERSION_ID] = #oldVersionId) AND ([APP_ID] = #appId) )
Can this Trigger be replace with a Foreign Key to update the VERSION_ID ?
What I think could be a problem is the AND condition, how to express that in a FK with On del/update Cascade?
FOREIGN KEY CONSTRAINTS don't update anything. They check the values being written to a record and cause the write to fail if they cause a constraint to fail.
Also, as #marc_s points out in his comment, triggers in MS SQL Server are set based. The INSERTED and DELETED tables can hold multiple records at once. Your code only works for one record.
You could try something along these lines...
UPDATE
table
SET
VERSION_ID = inserted.VERSION_ID
FROM
table
INNER JOIN
deleted
ON table.VERSION_ID = deleted.VERSION_ID
AND table.APP_ID = deleted.APP_ID
INNER JOIN
inserted
ON deleted.PRIMARY_KEY = inserted.PRIMARY_KEY
EDIT
I just read your comment, and I think I understand. You want a foreign key constraint with ON UPDATE CASCADE.
You use this format to create that with DDL.
ALTER TABLE DBO.<child table>
ADD CONSTRAINT <foreign key name> FOREIGN KEY <child column>
REFERENCES DBO.<parent table>(<parent column>)
{ON [DELETE|UPDATE] CASCADE}
Or you could just SQL Server Management Studio to set it up. Just make sure the ON UPDATE CASCADE is present.
I cannot really tell you what you're looking for - you're too unclear in your question.
But basically, if two tables are linked via a foreign key constraint, of course you can add a clause to that to make sure the child table gets updated when the parents table's PK changes:
ALTER TABLE dbo.ChildTable
ADD CONSTRAINT FK_ChildTable_ParentTable
FOREIGN KEY(ChildTableColumn) REFERENCES dbo.ParentTable(PKColumn)
ON UPDATE CASCADE
The ON UPDATE CASCADE does exactly that - if the referenced column (the PKColumn in ParentTable) changes, then the FK constraint will "cascade" that update down into the child table and update it's ChildTableColumn to match the new PKColumn
Read all about cascading referential integrity constraints and what options you have on MSDN Books Online