title: MySQL query - joining two tables producing duplicate results
body: <p>I'm running the following MySQL query in PHP.</p>
  
  <pre><code>"SELECT * 
  FROM `challenges`,`verifications` 
  WHERE (`challenges`.`user_id`='".$this-&gt;record['id']."' OR `challenges`.`opponent_id`='".$this-&gt;record['id']."') 
      AND `challenges`.`is_verified`='0' 
      AND (`challenges`.`status`='in-progress' OR `challenges`.`status`='pending') 
      AND 
      (
          (`verifications`.`user_id`='".$this-&gt;record['id']."' OR `verifications`.`opponent_id`='".$this-&gt;record['id']."') 
          AND (`verifications`.`user_verified`!=NULL AND `verifications`.`opponent_verified`=NULL) 
      ) 
  LIMIT 100";
  </code></pre>
  
  <p>This query is returning duplicate records for some reason.  If anyone has any insights, I would greatly appreciate it.</p>
  
  <p>Here is the structure for the two tables (challenges and verifications):</p>
  
  <p>Challenges Table:</p>
  
  <pre><code>CREATE TABLE `challenges` (
    `id` int(11) NOT NULL auto_increment,
    `wager` int(11) NOT NULL,
    `type` varchar(255) NOT NULL,
    `user_id` int(11) NOT NULL,
    `opponent_id` int(11) NOT NULL,
    `start_date` date NOT NULL,
    `date_created` timestamp NOT NULL default CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP,
    `start_time` time NOT NULL,
    `is_verified` tinyint(1) NOT NULL default '0',
    `status` varchar(255) NOT NULL default 'pending',
    `winner_id` int(11) default NULL,
    PRIMARY KEY  (`id`)
  ) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=0 ;
  </code></pre>
  
  <p>Verifications Table:</p>
  
  <pre><code>CREATE TABLE `verify` (
    `id` int(11) NOT NULL auto_increment,
    `user_id` int(11) NOT NULL,
    `opponent_id` int(11) NOT NULL,
    `challenge_id` int(11) NOT NULL,
    `user_verified` int(11) default NULL,
    `opponent_verified` int(11) default NULL,
    PRIMARY KEY  (`id`),
    UNIQUE KEY `challenge_id` (`challenge_id`)
  ) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=0;
  </code></pre>
  
  <p>Thanks for your help, and if you need any more info please let me know.</p>