MS SQL Server cross table constraint

Question

I have three tables:

1) Applications (AppId, Name)
2) Screen (ScreenId, Name)
3) Relation (AppId, ScreenId)

Now I want to apply some restrictions on related table: The same screen can be assigned to multiple application, but there cannot be two screens with same name that assigned to same application.

I know I can add Screen.Name to relation table and then create PK on AppId and Screen.Name, but I don't want such solution, since Screen.Name is subject to change.

What additional options I have to achieve such restriction?

Answer 1

You can create an indexed view based on the Relation and Screen tables and apply a unique constraint there.

create view DRI_UniqueScreens
with SCHEMABINDING
as
    select r.AppId,s.Name
    from
       [Schema].Relation r
         inner join
       [Schema].Screen s
         on
            r.ScreenId = s.ScreenId
GO
CREATE UNIQUE CLUSTERED INDEX IX_DRI_UniqueScreens
    on DRI_UniqueScreens (AppId,Name)