public function getStat()
{
 return $this->hasOne(UserStat::className(), ['user_id' => 'id']);
}

<?= GridView::widget([
 'dataProvider' => $dataProvider,
 'columns' => [

  //其他列
  
  [
   'label' => '统计数据',
   'value' => function($model){
    return isset($model->stat->data) ? $model->stat->data : null;
   }
  ],
  
  //其他列
 ],
]); ?>

public $data;
public function rules()
{/*{{{*/
 return [
  ['data'], 'integer'],
  //其他列
 ];
}/*}}}*/

public function search($params, $onlyActiveUsers = false)
{
 $query = User::find();
 $query->joinWith(['stat']);

 $dataProvider = new ActiveDataProvider([
  'query' => $query,
  'sort' => [
   'attributes' => [
    //其他列
    
    'data' => [
     'asc' => [UserStat::tableName() . '.data' => SORT_ASC],
     'desc' => [UserStat::tableName() . '.data' => SORT_DESC],
    ],
    
    //其他列
   ],
   'defaultOrder' => [
    'id' => SORT_DESC,
   ],
  ],
  'pagination' => [
   'pageSize' => 50,
  ],
 ]);

 $this->load($params);

 if (!$this->validate()) {
  $query->where('0=1');
  return $dataProvider;
 }

 $query->filterWhere([
 
  //其他列
  
  UserStat::tableName() . '.data' => $this->data
 ]);

 return $dataProvider;
}

<?= GridView::widget([
 'dataProvider' => $dataProvider,
 'columns' => [

  //其他列
  
  [
   'label' => '统计数据',
   'attribute' => 'data',
   'value' => function($model){
    return isset($model->stat->data) ? $model->stat->data : null;
   }
  ],
  
  //其他列
 ],
]); ?>

<?php $form = ActiveForm::begin(); ?>
//其他列 

<?= $form->field($model, 'data')?>

//其他列
<div class="form-group">
 <?= Html::submitButton('Search', ['class' => 'btn btn-primary']) ?>
</div>

<?php ActiveForm::end(); ?>

// 默认是这样的
public static function tableName()
{
 return 'user_stat';
}

public static function getDb()
{
 return Yii::$app->get('dbStat');
}

// 只需要在表明前添加数据库名
public static function tableName()
{
 return 'memory_stat.user_stat';
}

public static function getDb()
{
 return Yii::$app->get('dbStat');
}

// 为了提高代码稳定性，可以这样写
public static function tableName()
{
 preg_match("/dbname=([^;]+)/i", static::getDb()->dsn, $matches);
 return $matches[1].'.user_stat';
}

public static function getDb()
{
 return Yii::$app->get('dbStat');
}