怎么合并多个if条件

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if($start_id == $first_id && $arrive_id == '') {
                    echo "我是第一个城市城市";
                    //去查询第一个城市是否添加了交通工具
                    $start_id = '';
                    $arrive_id = $first_id;
                    $res = $this->model->get_traffic($tripid, $type, $start_id, $arrive_id);
                    if($res) {
                        $affected_rows = $this->model->update_traffic($traffic, $tripid, $type, $start_id, $arrive_id);
                        if($affected_rows > 0) {
                            echo "更新成功！";
                        }
                    }else{
                        $trafficid = $this->model->add_traffic($traffic, $tripid, $start_id, $arrive_id, $type, $dateline);
                        if($trafficid > 0) {
                            echo '添加成功';
                        }
                    }
                    exit;
                }
                if($start_id == $last_id && $arrive_id == '') {
                    echo "我是最后一个城市";
                    $start_id = $last_id;
                    $arrive_id = '';
                    $res = $this->model->get_traffic($tripid, $type, $start_id, $arrive_id);
                    
                    if($res) {
                        $affected_rows = $this->model->update_traffic($traffic, $tripid, $type, $start_id, $arrive_id);
                        if($affected_rows > 0) {
                            echo "更新成功！";
                        }
                    }else{
                        $trafficid = $this->model->add_traffic($traffic, $tripid, $start_id, $arrive_id, $type, $dateline);
                        if($trafficid > 0) {
                            echo '添加成功';
                        }
                    }
                    exit;
                }
                if($start_id == '' && $arrive_id == '') {
                    echo "需选择2个城市才能添加交通工具";
                }else{
                    echo "选择正确可以入库";
                    $res = $this->model->get_traffic($tripid, $type, $start_id, $arrive_id);
                    
                    if($res) {
                        $affected_rows = $this->model->update_traffic($traffic, $tripid, $type, $start_id, $arrive_id);
                        if($affected_rows > 0) {
                            echo "更新成功！";
                        }
                    }else{
                        $trafficid = $this->model->add_traffic($traffic, $tripid, $start_id, $arrive_id, $type, $dateline);
                        if($trafficid > 0) {
                            echo '添加成功';
                        }
                    }
                }
            }
            $this->display = true;
            $this->view->assign('cities', $cities);
            $this->view->assign('traffic', $_config['traffic']);
            $this->view->assign('tripid', $tripid);
            $this->view->assign('cityid', $cityid);
            $this->view->assign('type', $type);
        }else if($type == 2) {
            echo "我是来添加景点美食绿色的";
        }