SQL Server - Create an identifying relationship

Question

I'm currently designing a database to be implemented in SQL Server. I created the following tables without problem:

CREATE TABLE [Client] (
  [ClientId] INT NOT NULL,
  [Name] VARCHAR(45) NOT NULL,
  [IsEnabled] BIT NOT NULL DEFAULT 1,
  CONSTRAINT PK_TCASystem PRIMARY KEY CLUSTERED (
ClientId
 )
);

 CREATE TABLE [Configuration] (
  [ConfigId] INT NOT NULL,
  [ClientId] INT NOT NULL,
  [Name] VARCHAR(45) NOT NULL,
  CONSTRAINT PK_Configuration PRIMARY KEY CLUSTERED (
    ConfigId, ClientId
  ),
  CONSTRAINT "FK_SystemConfiguration" FOREIGN KEY 
  (
    ClientId
  ) REFERENCES [Client] (
    ClientId
  )
 );

However, when I tried to add this one:

CREATE TABLE [Mail] (
   [MailId] INT NOT NULL,
   [ConfigId] INT NOT NULL,
   [Recipient] VARCHAR(500) NOT NULL,
   [Sender] VARCHAR(50) NOT NULL,
   [Subject] VARCHAR(250) NOT NULL,
   [Message] TEXT NULL,

   CONSTRAINT PK_Mail PRIMARY KEY CLUSTERED (
    MailId, ConfigId
   ),
   CONSTRAINT "FK_ConfigurationMail" FOREIGN KEY 
   (
        ConfigId
   ) REFERENCES [Configuration] (
        ConfigId
   )
);

I got an error saying that There are no primary or candidate keys in the referenced table 'Configuration' that match the referencing column list in the foreign key 'FK_ConfigurationMail' . I believe this is because the constraint is trying to reference ConfigId , only one half of the composite key, and for this to work I'd need to reference the ClientId too, is that correct?

But my problem is that I first did the design for this database in MYSQL Workbench, and there I indicated that Configuration and Mail , as well as Client and Configuration , have a 1:n identifying relationship (because a Mail instance cannot be created if there isn't a Configuration instance first, and at the same time a Configuration instance cannot exist without having being assigned to a Client first), and as such it created the composite keys for Configuration and Mail . You can see a picture of that here .

So my question is, how can I translate this identifying relationship to SQL Server? Or is that not possible?

EDIT : As suggested I will remove the composite keys from the Configuration table, albeit my question still stands: If I have a 1:n identifying relationship where one of the tables involved uses composite keys, how can I display this on SQL Server? Or is such a case never supposed to happen?

2ND EDIT : To anyone who might come across this question, this post is well worth a read. Cleared up all my confusion in the matter.

Answer 1

Foreign key must reference PK (the entire PK, not portion of PK) or unique index. So add this between create table [Configuration] and [Mail].

CREATE UNIQUE NONCLUSTERED INDEX [UX_Configuration] ON [Configuration] ( [ConfigId] ASC )

Check out at sql fiddle for the whole working script: http://www.sqlfiddle.com/#!3/8877f