RT，这两个字段都是整形的时间戳数字，然后我使用下面方法：
$maps['lastime'] = ['exp', "lastime > respontime"];

结果：
Syntax error or access violation: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'lastime > respontime ) ORDER BY id desc LIMIT 6000' at line 1[/var/……/thinkphp/library/think/db/Connection.php:388]