Question

A same table foreign key constraint in my database is not accessible. I can not drop it, disable it, add it back, … How do I remove it and re-add it?

Note: I have several versions of my database all created with the same script. Only in one I see this behavior. In others, this key is easily added and removed.

Many thanks. Here is some scripts I ran and the result:

At some point in the past i ran the following script:

ALTER TABLE Recipe
ADD CONSTRAINT FK_Recipe_DuplicateOfRecipeId_Recipe_Id FOREIGN KEY (DuplicateOfRecipeId)
    REFERENCES Recipe (Id) ;

now running

ALTER TABLE Recipe DROP CONSTRAINT  FK_Recipe_DuplicateOfRecipeId_Recipe_Id 
results in the following error:
'FK_Recipe_DuplicateOfRecipeId_Recipe_Id' is not a constraint.

and running

ALTER TABLE Recipe NOCHECK CONSTRAINT FK_Recipe_DuplicateOfRecipeId_Recipe_Id
results in: Constraint 'FK_Recipe_DuplicateOfRecipeId_Recipe_Id' does not exist.

so i run

alter table Recipe ADD CONSTRAINT FK_Recipe_DuplicateOfRecipeId_Recipe_Id FOREIGN KEY (DuplicateOfRecipeId) REFERENCES Recipe (Id);

and i get:

The ALTER TABLE statement conflicted with the FOREIGN KEY SAME TABLE constraint "FK_Recipe_DuplicateOfRecipeId_Recipe_Id". The conflict occurred in database "CrawlerDB", table "dbo.Recipe", column 'Id'.

so I run:

select COUNT(*) from sys.objects where name = 'FK_Recipe_DuplicateOfRecipeId_Recipe_Id'
select COUNT(*) from sys.all_objects where name = 'FK_Recipe_DuplicateOfRecipeId_Recipe_Id'
SELECT COUNT(*) FROM sys.foreign_keys where name = 'FK_Recipe_DuplicateOfRecipeId_Recipe_Id'

and all 3 return nothing.

Whats going on and how do I fix it? I need to access this object, remove it and add it back.
Many thanks!

Answer 1

I’m guessing that your master database is corrupted. You’d probably be best suited by rebuilding it.

However, as a workaround, you could try this:

1. Duplicate your foreign key into a non-FK column

   ALTER TABLE Recipe ADD DuplicateOfFK INT

2. Copy all your FK data to the duplicate

   UPDATE Recipe SET DuplicateOfFK = DuplicateOfRecipeId

3. Drop the Foreign Key column

   ALTER TABLE Recipe DROP COLUMN DuplicateOfRecipeId

4. Go backwards.

   ALTER TABLE Recipe ADD DuplicateOfRecipeId INT

   UPDATE Recipe SET DuplicateOfRecipeId = DuplicateOfFK

   ALTER TABLE Recipe DROP COLUMN DuplicateOfFK

5. Add the constraint back.