Codeigniter中奇怪的内部服务器错误

Question

当查询似乎正常工作时，为什么会收到错误状态码500 Internal Server error？

这就是我发现的内容，当我在查询中删除->result();时，它返回状态200，这很好。但是，如果我在查询中添加->result();，则会出现内部服务器错误。

这是我的查询：

$this->db->select('message_tbl.id, message_tbl.message, message_tbl.date_created, message_sent.from_id, message_received.to_id, message_received.is_read');    
$this->db->from('message_tbl');
$this->db->join('message_received', 'message_received.msg_id = message_tbl.id');
$this->db->join('message_sent', 'message_sent.msg_id = message_tbl.id');
$this->db->where('message_sent.delete_status',0);
$this->db->where('message_received.delete_status',0);
$this->db->where('message_received.to_id',$this->user_id);
$this->db->where('message_received.parent_id',0);           
$query = $this->db->get()->result();