title: FK referencing PK with same column
body: <p>I was surprised to discover I can create a foreign key that refers to a primary key defined on the exact same table and column, for example:</p>
  
  <pre><code>ALTER TABLE dbo.Foo WITH CHECK ADD CONSTRAINT FK_Foo_Foo FOREIGN KEY(FooId)
  REFERENCES dbo.Foo (FooId)
  </code></pre>
  
  <p>I have a customer DB with such an FK defined and it seems completely redundant.</p>
  
  <p>Does it serve any purpose?</p>
  
  <p>NB. This is not the situation of a hierarchical relationship - the FK field is not a different field in the same table acting as a parent ID, but rather the PK field itself.</p>