title: Does dropping a table's unique key pose any problems in production?
body: <p>I'll expound a bit on my question, if I have a live database in production and I want to drop a Unique Key from one of the tables, be it a non-composite unique key or a composite one, will that pose any problems?</p>
  
  <p>I'm thinking this shouldn't pose any problems but I want to double check with the DB experts here.</p>
  
  <p>As for the composite unique key question, I want to drop it because I want to add a new column to that composite unique key.</p>
  
  <p>So this:</p>
  
  <pre><code>UNIQUE KEY `composite_key` (`username`, `email`),
  </code></pre>
  
  <p>Becomes this:</p>
  
  <pre><code>UNIQUE KEY `composite_key` (`username`, `email`, `age`),
  </code></pre>
  
  <p>Is there a way to "add" a column to the composite unique key? Or do I have drop it first and then define/add a new unique key composing of those 3 new columns? And again, will there be a problem if I do so?</p>
  
  <p>Thanks.</p>