1. 创建一个类来保存每列的最大/最小值

public class ColumnMinMax {
   private Double maxVal;
   private Double minVal;

   public ColumnMinMax(Double maxVal, Double minVal) {
       this.maxVal = maxVal;
       this.minVal = minVal;
   }

   public Double getMaxVal() {
       return maxVal;
   }

   public Double getMinVal() {
       return minVal;
   }
}

2. 创建一个DAO，执行查询并返回包含每列最大/最小值的列表

@Dao
public interface MyDao {
    @Query("SELECT MAX(column1) as max1, MIN(column1) as min1," +
            "MAX(column2) as max2, MIN(column2) as min2," +
            "MAX(column3) as max3, MIN(column3) as min3 " +
            "FROM my_table")
    LiveData> getColumnMinMax();
}

3. 在ViewModel中调用此DAO方法

public class MyViewModel extends ViewModel {
    private final LiveData> columnMinMaxLiveData;

    public MyViewModel(MyDao myDao) {
        columnMinMaxLiveData = myDao.getColumnMinMax();
    }

    public LiveData> getColumnMinMaxLiveData() {
        return columnMinMaxLiveData;
    }
}

4. 在Activity或Fragment中观察LiveData并使用数据

myViewModel.getColumnMinMaxLiveData().observe(this, columnMinMaxList -> {
    for (ColumnMinMax columnMinMax : columnMinMaxList) {
        Double max1 = columnMinMax.getMaxVal();
        Double min1 = columnMinMax.getMinVal();
        // Use the values as needed
    }
});