title: Prevent duplicated row SQL
body: <p>Let me explain in the current context:</p>
  
  <p>I have a <code>tokens</code> table which contains two columns: <code>name</code> and <code>token</code>.</p>
  
  <p>For example, a user named "John" can be assigned an "updated" token.</p>
  
  <p>However, I don't want to have two rows containing "John", "updated". However, there may be one line containing "Mathew", "updated", so primary keys cannot be used.</p>
  
  <p>Is it possible to do this without executing two statements? Thank you in advance.</p>