title: Default value of ondelete attibute of addForeignKeyConstraint liquibase
body: <p>According to this documentation:</p>
  
  <p><a href="http://www.liquibase.org/documentation/changes/add_foreign_key_constraint.html" rel="nofollow">http://www.liquibase.org/documentation/changes/add_foreign_key_constraint.html</a></p>
  
  <p>liquibase allows to create foreign keys. There is an interesting attribute there called <em>onDelete</em>. It is written that possible values are: 'CASCADE', 'SET NULL', 'SET DEFAULT', 'RESTRICT', 'NO ACTION', but it is not explicitly mentioned which one is <em>default</em> one.</p>
  
  <p>Any ideas? Or is it better just to mention it explicitly?</p>
  
  <p>I guess that it can depend on the database as well. I use PostgreSQL, MySQL and MsSQL.</p>