Foreign key referencing a 2 columns primary key in SQL Server
This question is pretty much similar to this one, but for SQL Server 2005 :
I have 2 tables in my database:
--'#' denotes the primary key [Libraries] #ID #Application Name 1 MyApp Title 1 2 MyApp Title 2 [Content] #ID Application LibraryID Content 10 MyApp 1 xxx 11 MyApp 1 yyy
(the database is obviously much more complex and having this double key makes sense)
Each library is identified by its unique ID and Application name. I'm trying to ensure that each content is properly referencing an existing library.
When creating the constraint (using the Wizard) as
Primary key table Foreign key table [Libraries] [Content] ID ---> LibraryID Application ---> Application
I have the following error:
The columns in table 'Libraries' do not match an existing primary key or UNIQUE constraint
Do you have any idea of what is going on? and if it's possible at all using SQL Server? (I can't modify the [Library] table at all)
Thanks a lot for your help!
Of course it's possible to create a foreign key relationship to a compound (more than one column) primary key. You didn't show us the statement you're using to try and create that relationship - it should be something like:
ALTER TABLE dbo.Content ADD CONSTRAINT FK_Content_Libraries FOREIGN KEY(LibraryID, Application) REFERENCES dbo.Libraries(ID, Application)
Is that what you're using?? If (ID, Application) is indeed the primary key on dbo.Libraries, this statement should definitely work.
Luk: just to check - can you run this statement in your database and report back what the output is??
SELECT tc.TABLE_NAME, tc.CONSTRAINT_NAME, ccu.COLUMN_NAME FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS tc INNER JOIN INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE ccu ON ccu.TABLE_NAME = tc.TABLE_NAME AND ccu.CONSTRAINT_NAME = tc.CONSTRAINT_NAME WHERE tc.TABLE_NAME IN ('Libraries', 'Content')
Note that the fields must be in the same order. If the Primary Key you are referencing is specified as (Application, ID) then your foreign key must reference (Application, ID) and NOT (ID, Application) as they are seen as two different keys.
The key is "the order of the column should be the same"
create Table A ( A_ID char(3) primary key, A_name char(10) primary key, A_desc desc char(50) ) create Table B ( B_ID char(3) primary key, B_A_ID char(3), B_A_Name char(10), constraint [Fk_B_01] foreign key (B_A_ID,B_A_Name) references A(A_ID,A_Name) )
the column order on table A should be --> A_ID then A_Name; defining the foreign key should follow the same order as well.
The Content table likely to have multiple duplicate Application values that can't be mapped to Libraries. Is it possible to drop the Application column from the Libraries Primary Key Index and add it as a Unique Key Index instead?
I had the same problem and I think I have the solution.
If your field Application in table Library has a foreign key that references a field in another table (named Application I would bet), then your field Application in table Library has to have a foreign key to table Application too.
After that you can do your composed foreign key.
Excuse my poor english, and sorry if I'm wrong.