title: Mysql Unknown column in where clause
body: <pre><code>SELECT t1.`ID`, t1.`notification_type`, t1.`notification_by`, t1.`notification_by_username`, 
                  t1.`notification_status`, t1.`notification_date`, t1.`school_key`, t1.`class_key`, t1.`post_key`, t1.`extra`, t1.`class_info`, t1.`class_subject`,
                  (SELECT `notification_last_check` 
                         FROM data_users.account_info t2
                         WHERE t2.`user_key` = t1.`notification_by` LIMIT 1) AS `notification_last_check` 
         FROM `14754931095281411` t1 
         WHERE t1.`notification_status` = '10' 
                  AND t1.`notification_date` &gt; t2.`notification_last_check`   
         ORDER BY `notification_date` DESC LIMIT 10;
  </code></pre>
  
  <blockquote>
    <h1>1054 - Unknown column 't2.notification_last_check' in 'where clause'</h1>
  </blockquote>
  
  <p>why im getting the above error ?</p>