title: using left join along with 'IS NULL'
body: <p>I came across this query to get a row having max value. Can you explain how this works</p>
  
  <pre><code>SELECT s1.article, s1.dealer, s1.price, s2.article, s2.dealer, s2.price
  FROM shop s1
  LEFT JOIN shop s2 ON s1.price &lt; s2.price
  WHERE s2.article IS NULL;
  </code></pre>
  
  <p>Dump : </p>
  
  <pre><code>CREATE TABLE `shop` (
  `article` int(4) unsigned zerofill NOT NULL DEFAULT '0000',
  `dealer` char(20) NOT NULL DEFAULT '',
  `price` double(16,2) NOT NULL DEFAULT '0.00',
  PRIMARY KEY (`article`,`dealer`)
  ) ENGINE=InnoDB DEFAULT CHARSET=utf8;
  
  INSERT INTO `shop` VALUES 
  (0001,'A',3.45), (0001,'B',3.99), 
  (0002,'A',10.99),(0003,'B',1.45),
  (0003,'C',1.69),(0003,'D',1.25),
  (0004,'D',19.95);
  </code></pre>