title: Error on MySQL server with duplicate colunm name
body: <p>I am getting this error:</p>
  
  <pre><code>    Notice: Error: Duplicate column name 'color' 
  Error No: 1060
  ALTER TABLE oc_hj_import ADD COLUMN (`color` BLOB NOT NULL ) in D:\xampp\htdocs\upload\system\database\mysql.php on line 50
  </code></pre>
  
  <p>This is the code:</p>
  
  <pre><code>public function alterImportTable($new_fields) {
      if (!empty($new_fields)) {
          $sql = "ALTER TABLE " . DB_PREFIX . "hj_import ADD COLUMN ";
          $fields_sql = array();
          foreach ($new_fields as $field) {
              $fields_sql[] = '`' . $field . "` BLOB NOT NULL ";
          }
          $sql .= '(' . implode(', ', $fields_sql) . ')';
          $sql = str_replace(', )', ')', $sql);
          $this-&gt;db-&gt;query($sql);
      }
  }
  </code></pre>
  
  <p>How can I fix that?</p>