Here is an example of creating a primary key using the CONSTRAINT keyword:

CREATE TABLE Persons(PersonID COUNTER(1,1) NOT NULL,
                     FirstName varchar(20),
                     LastName varchar(20) NOT NULL,
                     CONSTRAINT PK_People PRIMARY KEY(PersonID));

Here is an example that adds uses a constraint to add a primary key:

Here is an example:

Private Sub cmdMakePrimaryKey_Click()
    DoCmd.RunSQL "ALTER TABLE Departments " & _
                 "ADD CONSTRAINT PK_Departments PRIMARY KEY(DepartmentCode);"
End Sub