title: Unique key not working
body: <p>I have a table cars, which gets populated with the joined data of table cars1 and cars2.
  The schema looks like this:</p>
  
  <pre><code> CREATE TABLE `cars` (
     `id` int(10) NOT NULL AUTO_INCREMENT,
     `uniqueid` varchar(10) NOT NULL,
     `name` varchar(20) NOT NULL
     UNIQUE KEY `uniqueid` (`uniqueid`)
   ) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=latin1
  </code></pre>
  
  <p>However, I have duplicate entries for the uniqueid field in my table:</p>
  
  <pre><code> ID     UNIQUEID     NAME
   1      1            Mercedes
   2      2            Audi
   3      2            Chevrolet
  </code></pre>
  
  <p>The data get's populated in that table from cars1 and cars2 with simple INSERT IGNORE INTO SELECT FROM statement.</p>
  
  <p>How is this even possible? Could it be that the index of the table is corrupt? I came across that duplicate rows by doing:</p>
  
  <pre><code> SELECT uniqueid, COUNT(uniqueid) FROM cars GROUP BY uniqueid HAVING(COUNT(uniqueid)&gt;1);
  </code></pre>
  
  <p>How can I fix that issue?</p>