title: how to delete duplicate entry by one SQL?
body: <p>i has a table <code>deal</code>:</p>
  
  <pre><code>CREATE TABLE `deal` (
    `id` int(11) NOT NULL auto_increment,
    `site` int(11) NOT NULL default '0',
    `area` int(11) NOT NULL default '0',
    `name` varchar(255) default NULL,
    PRIMARY KEY  (`id`)
  );
  </code></pre>
  
  <p>i want to create :</p>
  
  <pre><code>UNIQUE KEY `site` (`site`,`area`,`name`);
  </code></pre>
  
  <p>but now, <code>name</code> filed is not UNIQUE,when i create this key,i get error:</p>
  
  <pre><code>duplicate entry 'aaa' for key 2
  </code></pre>
  
  <p>my table datas:</p>
  
  <pre><code>Data
  id site  area  name
  ---------------------------------
  1  site1 area1 aaa
  2  site1 area2 bbb
  3  site1 area1 aaa   &lt;&lt;&lt;&lt; i want delete this
  4  site2 area1 ccc
  5  site2 area1 ccc   &lt;&lt;&lt;&lt; i want delete this
  ...
  </code></pre>
  
  <p>how to do it by one sql string?</p>
  
  <p>thanks for your help :)</p>