Error 1064 SQL Syntax

Question

I'm getting error 1064.

You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'ORDER BY d3.doctor_id DESC' at line 7

Line Number: 81

Line 81 is below:-

d3.doctor_status="Y" AND d7.city_id ='.$city.' ORDER BY d3.doctor_id DESC');

    public function doctor_similar($q){
        if(count($q)>0) {
            $spc_id='';
        $city=($this->session->userdata('city_id'));
            foreach ($q as $res_spc) { 
            $spc_id.=$res_spc['department_id'].',';             
        }
        $list=rtrim($spc_id,",");
        $query = $this->db->query('SELECT DISTINCT d3.doctor_id,d3.doctor_name,d3.doctor_specialization FROM Dr_doctors_list AS d3
            JOIN Dr_doctors_spec as d2 ON d2.doctor_id = d3.doctor_id                           
            JOIN Dr_doctors_hosp as d4 ON d3.doctor_id = d4.doctor_id
            JOIN Dr_hospital_lists as d5 ON d4.hospital_id = d5.hospital_id
            JOIN Dr_city_list as d7 ON d5.hospital_city = d7.city_id
            WHERE d2.department_id IN ( '.$list.' )  AND 
            d3.doctor_status="Y" AND d7.city_id ='.$city.' ORDER BY d3.doctor_id DESC');

        return $query->result_array();
        } else {
            return '';

        }
    }