Laravel/Eloquent，动态检索数据（whereIn，sum）

Question

我是 Laravel 的菜鸟，我想以“自动”的方式从数据库中检索数据。我有一个查询，可以获取“状态”是最新重复的关键“案例”的值

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

但我想用 whereIn 来做这个

$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');

但似乎这个遍历 $statesArr 并且只获得最后一个值，这是正确的，但只是一个状态的一个值，我想要来自所有状态的所有值

编辑、样本数据和预期输出

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

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

这是 ALABAMA 最后一次出现，所以我想获取该行的案例值，每个州的 THIS。所以我可以创建一个面板，我可以在其中显示州名称及其价值案例和死亡人数，而无需对每个州进行查询。

Answer 1

要为每个状态选择最新条目（基于最新的 autoincrement id），您可以与您的表进行自我连接，例如

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();

如果你使用的是最新版本的 laravel，你可以使用内部连接重写上面的代码

$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();

或者你可以使用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();

Answer 2

试试这样：

$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');