Mysqli错误:列计数与第1行的值计数不匹配

下面是正在执行的mysqli查询，任何人都知道我得到了这样的错误:

Below is the mysqli query that is being performed, anyone know what I get such error:

$sql = mysqli_query($db, "INSERT INTO `tbl_bugzilla` 
    (`id`, `by`, `title`, `content`, `date`, `application`,`priority`, `assigned`, `status`) 
    VALUES (NULL, '".$_SESSION['exp_user']['username']."', '"
        .$_SESSION['exp_user']['username']."', '".$title."', '".$content."','"
        .$dt."', '".$_POST['app']."', '".$_POST['priority']."', 'Unassigned', 'Unconfirmed')");

错误: 列数与第1行的值计数不符

更重要的是，您能解释一下错误，这样我就不会再犯同样的错误了吗?

More importantly, could you explain the error so I don't make the same mistake again?

谢谢