如何在Codeigniter中的LEFT JOIN中修复子查询？

Question

我尝试添加JOIN子查询：

    $this->db->join('stocks AS stn', 'stn.stocksIdMF = 
    (SELECT medicalfacilities.MedicalFacilitiesIdUser 
            FROM medicalfacilities 
            WHERE medicalfacilities.MedicalFacilitiesIdUser = stn.stocksIdMF AND stn.stocksEndDate >= UNIX_TIMESTAMP()
        ORDER BY stn.stocksId DESC LIMIT 1)',
'LEFT', false);'

但Codeigniter破坏了这个查询。查询有什么问题？ 可能以某种方式替换此查询？