title: mysql structure double unique
body: <p>I am trying to make a mysql table and have got stuck with making it.</p>
  
  <p>2 columns required:</p>
  
  <pre><code>aid
  bid
  </code></pre>
  
  <p>The trick is aid is not unique and bid is not unique, but the combination of aid-bid IS unique.</p>
  
  <p>EG:</p>
  
  <pre><code>a b ok?
  0 1 y
  0 2 y
  0 7 y
  1 1 y
  1 7 y
  8 3 y
  0 7 N - since 0 7 is already in table...
  </code></pre>
  
  <p>How can I make this table in sql so it works?</p>