title: SQL Query not working due to column name error however column exists
body: <p>I am having a problem with the query below:</p>
  
  <pre><code>SELECT *
  FROM `pageindex`
      FULL JOIN `pages` ON `pageindex`.`url` = `pages`.`page`
  WHERE `pageindex`.`url` IS NULL;
  </code></pre>
  
  <p>I have also tried this:</p>
  
  <pre><code>SELECT *
  FROM pageindex
      FULL JOIN pages ON pageindex.url = pages.page
  WHERE pageindex.url IS NULL;
  </code></pre>
  
  <p>I get this error:</p>
  
  <pre><code>ERROR 1054 (42S22): Unknown column 'pageindex.url' in 'where clause'
  </code></pre>
  
  <p>But I'm not understanding why, when the column does exist, here is the columns from the table:</p>
  
  <pre><code>+--------------+--------------+------+-----+---------+-------+
  | Field        | Type         | Null | Key | Default | Extra |
  +--------------+--------------+------+-----+---------+-------+
  | url          | varchar(255) | NO   | PRI | NULL    |       |
  | title        | varchar(255) | YES  | MUL | NULL    |       |
  | keywords     | text         | YES  |     | NULL    |       |
  | description  | text         | YES  |     | NULL    |       |
  | last_updated | date         | YES  |     | NULL    |       |
  | heading      | varchar(255) | YES  |     | NULL    |       |
  | textcontent  | text         | YES  |     | NULL    |       |
  | htmlcontent  | text         | YES  |     | NULL    |       |
  | audiencetype | varchar(255) | YES  |     | NULL    |       |
  +--------------+--------------+------+-----+---------+-------+
  </code></pre>
  
  <p>Hope you can help, </p>
  
  <p>Thanks</p>