Laravel 连表查询报语法错误，拿 sql 到数据库执行正常

        $model = new Curriculum;
        $data['data'] = $model->setTable('c')
            ->from('curriculums as c')
            ->select(DB::raw('c.*,GROUP_CONCAT(cp.position_id) AS position_ids'))
            ->where('c.c_id',$user_info['c_id'])
            ->where('c.is_del',0)
            ->leftJoin('curriculum_position as cp', 'c.id', '=', 'cp.curriculum_id')
//            ->when($keyword, function ($query) use ($keyword) {
//                return $query->where('c.name','like','%'.$keyword.'%');
//            })
            ->groupBy('c.id')
            ->orderBy('c.created_at','DESC')
            ->skip($skip)->take($limit)->get()->toArray();Copy

        $sql_pre = "SELECT c.*,GROUP_CONCAT(cp.position_id) as position_ids 
                    FROM curriculums AS c 
                    LEFT JOIN curriculum_position AS cp ON c.id = cp.curriculum_id
                    WHERE c.c_id = 12 AND c.is_del = 0 ";

//        if ($keyword){
//            $sql_pre .= " AND c.name LIKE \'%$keyword%\' ";
//        }

        $sql_suf = "GROUP BY c.id ORDER BY c.created_at DESC LIMIT $limit OFFSET $skip";

        $sql = $sql_pre.$sql_suf;
        $res = DB::select($sql);Copy