Adding 2 primary keys in mdf database in VS Community 2013 from Server Explorer

Question

Hello,
I have to update a Windows Forms application using VS Community 2013. I have to add a little database with customers and installations, so 1 customer can manage many installations and 1 installation can be managed by many customers. It is the first
time that use VS 2013 so I don't know if I have done all steps well:
Right click in the project item -> Add -> New item -> Data -> Service-base Database. I don't know what "service-based" means, but is the only way I can see to add a database. This step added
mydb.mdf file to the project.
Server Explorer -> Data Connections -> mydb.mdf -> Right click on Tables -> Add New Table. I have added
Customer and Installation tables with no problem. These are T-SQL scripts:
CREATE TABLE [dbo].[Customer]
[UserName] NVARCHAR(50) NOT NULL PRIMARY KEY,
[Password] NVARCHAR(50) NOT NULL,
[FullName] NVARCHAR(50) NOT NULL,
[Company] NVARCHAR(50) NULL,
[Contact] NVARCHAR(100) NULL
CREATE TABLE [dbo].[Installation]
[Imei] NVARCHAR(15) NOT NULL PRIMARY KEY,
[Ip] NVARCHAR(15) NOT NULL,
[Name] NVARCHAR(50) NOT NULL
Now, I have to create CustomerInstallation table with 2 primary keys. The script:
CREATE TABLE [dbo].[CustomerInstallation]
[UserName] NVARCHAR(50) NOT NULL ,
[Imei] NVARCHAR(15) NOT NULL,
PRIMARY KEY ([UserName]),
PRIMARY KEY ([Imei]),
CONSTRAINT [FK_CustomerInstallation_Customer] FOREIGN KEY ([UserName]) REFERENCES [Customer]([UserName]),
CONSTRAINT [FK_CustomerInstallation_Installation] FOREIGN KEY ([Imei]) REFERENCES [Installation]([Imei])
When I click the Update button, I get the following error message:
Update cannot proceed due to validation errors.
Please correct the following errors and try again.
SQL71533 :: A table or table-valued function ([dbo].[CustomerInstallation]) contains more than one primary key.
SQL71531 :: The table or view ([dbo].[CustomerInstallation]) has more than one clustered index.
So my question is: How can I add 2 primary keys to the table? Is it posible with this "service-based" database?
Thank you for all,
Jon.
PD: I didn't know in what forum write this question, please, move this thread to the appropriate forum. Sorry for the inconvenience.

Answer 1

You can only have one primary key per table but the primary key can be over multiple columns so:
CREATE TABLE [dbo].[CustomerInstallation]
    [UserName] NVARCHAR(50) NOT NULL , 
    [Imei] NVARCHAR(15) NOT NULL, 
    PRIMARY KEY ([UserName], [Imei]),    
    CONSTRAINT [FK_CustomerInstallation_Customer] FOREIGN KEY ([UserName]) REFERENCES [Customer]([UserName]),
    CONSTRAINT [FK_CustomerInstallation_Installation] FOREIGN KEY ([Imei]) REFERENCES [Installation]([Imei])
will let you have both columns as part of the primary key