title: MySQL: is primary key unique by default?
body: <p>If I define a column as a <em>primary key</em> in MySQL, is it also <em>unique key</em> by default or do I need to also define it as <em>unique key</em> (in case I want it to be unique)?</p>
  <p>I saw this question <a href="https://stackoverflow.com/questions/2973420/what-is-the-difference-b-w-primary-key-and-unique-key">What is the difference b/w Primary Key and Unique Key</a> that explain the difference between the two, but doesn't exactly answer my question.</p>
  <p>Does PK is UK by default or I need to explicitly define it?</p>