Вариант 1
create table Positions(
  Id int not null primary key identity,
  _Name nvarchar(100) not null check(_Name <> N'')
);
go


create table Emp(
  Id int not null primary key identity,
  _Name nvarchar(100) not null check(_Name <> N''),
  PositionId int not null foreign key references Positions(Id)
)

Вариант  2
create table Emp(
  Id int not null primary key identity,
  _Name nvarchar(100) not null check(_Name <> N''),
  Position nvarchar(100) not null check(_Name <> N'')
)