title: MySQL - Make a pair of values unique
body: <p>I have a table with two int values that are IDs. On their own these IDs can show up any number of times in the table, but together they should only ever appear once.</p>
  
  <p><strong>Is there a way to make a pair of values unique and still allow the individual values to show up multiple times?</strong></p>
  
  <p>As a follow up, if this is possible can the pair of values be used as a key? I currently have a 3rd column for a unique auto increment value for my key.</p>