Java Android-契约和提供者加入交互

我只是想了解在Udacity Android课程中我的代码中发生了什么

当我使用一种类型的URI时，JOIN语句起作用，但是如果我使用另一种类型的URI，JOIN就不起作用，我不明白为什么

1-）当我加入时，它工作：

String sortOrder = WeatherContract.WeatherEntry.COLUMN_DATETEXT + " ASC";
    mLocation = settings.getLocation();
    Uri weatherForLocationUri = WeatherContract.WeatherEntry.buildWeatherLocationWithDate(
            mLocation, DATE_KEY);
    Log.e("URI_REQUISITE", weatherForLocationUri.toString());

    return new CursorLoader(
            getActivity(),
            weatherForLocationUri,
            new String[] {
                WeatherContract.WeatherEntry.COLUMN_SHORT_DESC,
                WeatherContract.WeatherEntry.COLUMN_MAX_TEMP,
                WeatherContract.WeatherEntry.COLUMN_MIN_TEMP,
                WeatherContract.WeatherEntry.COLUMN_HUMIDITY,
                WeatherContract.WeatherEntry.COLUMN_WIND_SPEED,
                WeatherContract.WeatherEntry.COLUMN_WEATHER_ID,
                WeatherContract.WeatherEntry.COLUMN_PRESSURE,
                WeatherContract.WeatherEntry.COLUMN_DEGREES,
                WeatherContract.LocationEntry.COLUMN_LOCATION_SETTINGS // <- this row is the problem
                //^ this row is the problem
            },
            null,
            null,
            sortOrder
    );

String sortOrder=WeatherContract.WeatherEntry.COLUMN\u DATETEXT+“ASC”；
mLocation=settings.getLocation（）；
Uri weatherForLocationUri=WeatherContract.WeatherEntry.buildWeatherLocationWithDate(
M位置、日期（U键）；
Log.e（“URI_REQUISITE”，weatherForLocationUri.toString（））；
返回新游标装入器(
getActivity（），
weatherForLocationUri，
新字符串[]{
WeatherContract.WeatherEntry.COLUMN_SHORT_DESC，
WeatherContract.WeatherEntry.COLUMN_MAX_TEMP，
WeatherContract.WeatherEntry.COLUMN\u MIN\u TEMP，
WeatherContract.WeatherEntry.COLUMN_湿度，
WeatherContract.WeatherEntry.COLUMN\u风速，
WeatherContract.WeatherEntry.COLUMN\u WEATHER\u ID，
WeatherContract.WeatherEntry.COLUMN_压力，
WeatherContract.WeatherEntry.COLUMN_度，
WeatherContract.LocationEntry.COLUMN\u LOCATION\u SETTINGS//客观地说，这就是我问题的答案

SQLiteQueryBuilder->setTables->

String sortOrder = WeatherContract.WeatherEntry.COLUMN_DATETEXT + " ASC";
    return new CursorLoader(
            getActivity(),
            WeatherContract.LocationEntry.CONTENT_URI,
            new String[] {
                WeatherContract.WeatherEntry.COLUMN_SHORT_DESC,
                WeatherContract.WeatherEntry.COLUMN_MAX_TEMP,
                WeatherContract.WeatherEntry.COLUMN_MIN_TEMP,
                WeatherContract.WeatherEntry.COLUMN_HUMIDITY,
                WeatherContract.WeatherEntry.COLUMN_WIND_SPEED,
                WeatherContract.WeatherEntry.COLUMN_WEATHER_ID,
                WeatherContract.WeatherEntry.COLUMN_PRESSURE,
                WeatherContract.WeatherEntry.COLUMN_DEGREES,
                WeatherContract.LocationEntry.COLUMN_LOCATION_SETTINGS // <- this row is the problem
                //^ this row is the problem
            },
            WeatherEntry.COLUMN_DATETEXT+" = ?",
            new String []{DATE_KEY},
            sortOrder
    );