函数delete_img不起作用

Question

我按照链接 https://github.com/blueimp/jQuery-File-Upload/wiki/Working-with-databases

所有工作除了函数del_img()

function delete_img($delimg)
{
    $delete_from_db = $this->query("DELETE FROM files WHERE file = '$delimg'") or die(mysql_error());
    return $delete_from_db;
}

我不明白为什么它不起作用