MySql子查询访问父左连接

Question

SELECT t1.`ID`, 
      `notification_type`,
      `notification_by`,
      `notification_by_username`,
      `notification_status`, 
      `notification_date`, 
      `school_key`,
      t1.`class_key`, `post_key`,t2.`class_number` ,t2.`class_section`,t2.`class_subject` FROM `3254534545` t1
      LEFT JOIN `schools_classes.t1.school_key` t2
      ON t2.`class_key`= t1.`class_key` ORDER BY t1.`notification_date` DESC;

我怎样才能获得schools_classes。t1.school_key值，这是表名.t1.school_key结果应为：364551436

我收到此错误

  

1146 - 表'schools_classes.t1.school_key'不存在