Laravel / Eloquent，以二维方式检索数据其中，求和

如何解决Laravel / Eloquent，以二维方式检索数据其中，求和

我在Laravel中是个菜鸟，我想以一种“自动化”的方式从数据库中检索数据。我有一个查询，它获取键“ cases”的值，其中“ state”是最近重复的

$pieWyoming=State::select('cases')->where('state','=','Wyoming')->orderByDesc('id')->limit(1)->get()->sum('cases');

但是我想用whereIn

$statesArr = array("Alabama","Alaska","Arizona","Arkansas","California","Colorado","Connecticut","Delaware","District of Columbia","Florida","Georgia","Guam","Hawaii","Idaho","Illinois","Indiana","Iowa","Kansas","Kentucky","Louisiana","Maine","Maryland","Massachusetts","Michigan","Minnesota","Mississippi","Missouri","Montana","Nebraska","Nevada","New Hampshire","New Jersey","New Mexico","New York","North Carolina","North Dakota","Northern Mariana Islands","Ohio","Oklahoma","Oregon","Pennsylvania","Puerto Rico","Rhode Island","South Carolina","South Dakota","Tennessee","Texas","Utah","Vermont","Virgin Islands","Virginia","Washington","West Virginia","Wisconsin","Wyoming");

$Wyoming=State::select('cases')->whereIn('state',$statesArr)->orderByDesc('id')->limit(1)->get()->sum('cases');

但是似乎遍历$ statesArr并仅获取最后一个值，这是正确的，但仅是一个状态的一个值，我希望所有状态的所有值

编辑，示例数​​据和预期输出

数据库保存数据https://res.cloudinary.com/dcdajhifi/image/upload/v1599003808/ex1_ys5ksi.png

并且我想只获取数组$ statesArr中每个状态的字段“ cases”的值，例如，每个状态应该是最后一个重复的状态 https://res.cloudinary.com/dcdajhifi/image/upload/v1599003808/ex2_lby8md.png

这是ALABAMA的最后一次出现，所以我想获取此行的案例值，即每个州的情况。因此，我可以创建一个面板，在其中显示州名称及其值的大小写和死亡，而无需查询每个州。

解决方法

尝试这样：

$statesArr = array("Alabama","Alaska","Arizona","Arkansas","California","Colorado","Connecticut","Delaware","District of Columbia","Florida","Georgia","Guam","Hawaii","Idaho","Illinois","Indiana","Iowa","Kansas","Kentucky","Louisiana","Maine","Maryland","Massachusetts","Michigan","Minnesota","Mississippi","Missouri","Montana","Nebraska","Nevada","New Hampshire","New Jersey","New Mexico","New York","North Carolina","North Dakota","Northern Mariana Islands","Ohio","Oklahoma","Oregon","Pennsylvania","Puerto Rico","Rhode Island","South Carolina","South Dakota","Tennessee","Texas","Utah","Vermont","Virgin Islands","Virginia","Washington","West Virginia","Wisconsin","Wyoming");

$Wyoming = State::whereIn('state',$statesArr)->orderByDesc('id')->sum('cases');

,

要为每个州选择最新条目（基于最新的自动增量 ID），您可以像这样对表进行自连接

DB::table('states as a')
  ->select('a.*')
  ->leftJoin('states as b',function ($join) {
        $join->on('a.state','=','b.state')
             ->whereRaw(DB::raw('a.id < b.id'))
             ;
   })
  ->whereNull('b.id')
  ->whereIn('a.state',$statesArr)
  ->get();

如果您使用的是最新版本的laravel，则可以使用内部联接在上面重写

$latestStates = DB::table('states')
                   ->select(DB::raw('max(id) as max_id'))
                   ->groupBy('state');

$states = DB::table('states as a')
        ->joinSub($latestStates,'b',function ($join) {
            $join->on('a.id','b.max_id');
        })->whereIn('a.state',$statesArr)
          ->get();

或者您可以使用whereExists

$states = DB::table('states as a')
           ->whereExists(function ($query) {
               $query->select(DB::raw(1))
                     ->from('states as b')
                     ->whereRaw('a.state= b.state')
                     ->groupBy('b.state')
                     ->havingRaw('max(b.id) = a.id')
                     ;
           })->whereIn('a.state',$statesArr)
             ->get();