title: SQL Foreign Key without constraints the same as ON DELETE RESTRICT?
body: <p>I found the following two SQL schemas in an old exam. The exam does not seem to stick with one specific SQL syntax, but I hope this shouldn't matter for this question: What is the difference between <code>ON DELETE RESTRICT</code> and having just a Foreign Key without any such trigger clause?</p>
  
  <pre><code>-- Schema B --
  CREATE TABLE tab1 (
  tab1_key INT
  NOT NULL UNIQUE ) ;
  CREATE TABLE tab2 (
  tab2_ref INT NOT NULL,
  FOREIGN KEY ( tab2_ref )
  REFERENCES tab1 ( tab1_key ) ) ;
  
  -- Schema C --
  CREATE TABLE tab1 (
  tab1_key INT
  NOT NULL UNIQUE ) ;
  CREATE TABLE tab2 (
  tab2_ref INT NOT NULL,
  FOREIGN KEY ( tab2_ref )
  REFERENCES tab1 ( tab1_key )
  ON DELETE RESTRICT
  ON UPDATE NO ACTION ) ;
  </code></pre>
  
  <p>I would assume that the only difference between those two schemas is the last line in Schema C, but I cannot find any documentation on using Foreign Key without any additional constraint. So is this assumption correct?</p>
  
  <p><sup>I attempted to try those in pgAdmin, but that program keeps failing (and seems to be known for its bugs) so I figured asking here is less effort than debugging that tool.</sup></p>
  
  <p><sup>Also, please note that while these Schemas are from an old exam, this question is not the same as the exam question. Otherwise I would look at the solutions.
   This is <em>not</em> homework.</sup></p>