title: Default behavior in mysql on delete
body: <p>If I do this</p>
  
  <pre><code>ALTER TABLE `table`
  ADD CONSTRAINT `FK_table` 
  FOREIGN KEY (`IDtable`) 
  REFERENCES `table2` (`ID`) 
  ON UPDATE CASCADE;
  </code></pre>
  
  <p>What is default behavior for ON DELETE? Is it restrict, cascade, set null?</p>