title: "No unique identifier for this row." in Postgres when trying to delete a row
body: <p>I've got a simple table with the following scheme:</p>
  
  <pre><code>CREATE TABLE dateien(
      id int PRIMARY KEY UNIQUE DEFAULT NEXTVAL('dateien_id_seq'),
      name varchar(64),
      zeit timestamp DEFAULT now(),
      groesse float,
      dateityp_id int references dateitypen(id),
      benutzer_id int references benutzer(id)
  );
  </code></pre>
  
  <p>When trying to delete a row via phppgadmin I always get the message:
  <code>No unique identifier for this row.</code></p>
  
  <p>Also via pure sql there is no effect after the delete statement.
  Can you tell me what the problem is?</p>