我试图返回一个用户列表，按用户最近一行的字段(pt_seen)排序。这有意义吗？到目前为止我有:SELECTu.users_id,u.username,ed.dateFROMusersuLEFTJOINexercises_doneedONed.user_id=u.users_idWHEREu.pt_id=1GROUPBYu.users_id这显然只返回分组的用户。表格如下所示:users:users_id|pt_id|username1|1|billy2|1|bob3|1|sueexercises_done:exercises_done_id|user_id|pt_id|exercis

我正在尝试在Laravel5.5中设置数据库事务，但它似乎不起作用。我使用MySQL5.7.20，tools模式中的所有表都是InnoDB。我也在运行PHP7.2.3。我有这个代码:DB::beginTransaction();try{//checkswhethertheusersmarkedforremovalarealreadyassignedtothelistforeach($removeStudentsas$removeStudent){if($ls->allocatedStudents->find($removeStudent->id)===null){thrownewExc

我有以下Controller方法:@RequestMapping(produces=MediaType.APPLICATION_JSON_VALUE,value="session/{id}/exercises")publicResponseEntity>exercises(@PathVariable("id")Longid){Optionalopt=sessionRepository.findWithExercises(id);Setexercises=Sets.newLinkedHashSet();if(opt.isPresent()){exercises.addAll(opt.ge

我有以下Controller方法:@RequestMapping(produces=MediaType.APPLICATION_JSON_VALUE,value="session/{id}/exercises")publicResponseEntity>exercises(@PathVariable("id")Longid){Optionalopt=sessionRepository.findWithExercises(id);Setexercises=Sets.newLinkedHashSet();if(opt.isPresent()){exercises.addAll(opt.ge