配置单元查询结果中的列名称为空

Question

我已经从NOAA下载了Weath.txt文件，看起来像：

WBAN,Date,Time,StationType,SkyCondition,SkyConditionFlag,Visibility,VisibilityFlag,WeatherType,WeatherTypeFlag,DryBulbFarenheit,DryBulbFarenheitFlag,DryBulbCelsius,DryBulbCelsiusFlag,WetBulbFarenheit,WetBulbFarenheitFlag,WetBulbCelsius,WetBulbCelsiusFlag,DewPointFarenheit,DewPointFarenheitFlag,DewPointCelsius,DewPointCelsiusFlag,RelativeHumidity,RelativeHumidityFlag,WindSpeed,WindSpeedFlag,WindDirection,WindDirectionFlag,ValueForWindCharacter,ValueForWindCharacterFlag,StationPressure,StationPressureFlag,PressureTendency,PressureTendencyFlag,PressureChange,PressureChangeFlag,SeaLevelPressure,SeaLevelPressureFlag,RecordType,RecordTypeFlag,HourlyPrecip,HourlyPrecipFlag,Altimeter,AltimeterFlag
00102,20150101,0001,0,OVC043, ,10.00, , , ,27, ,-2.8, ,26, ,-3.1, ,25, ,-3.9, , 92, , 0, ,000, , , ,30.05, , , , , ,30.36, ,AA, , , ,30.23, 
00102,20150101,0101,0,OVC045, ,10.00, , , ,27, ,-2.8, ,26, ,-3.1, ,25, ,-3.9, , 92, , 6, ,080, , , ,30.07, , , , , ,30.37, ,AA, , , ,30.25, 
00102,20150101,0201,0,OVC047, ,10.00, , , ,26, ,-3.3, ,25, ,-3.7, ,24, ,-4.4, , 92, , 6, ,090, , , ,30.08, , , , , ,30.39, ,AA, , , ,30.26, 
00102,20150101,0301,0,OVC049, ,10.00, , , ,26, ,-3.3, ,25, ,-3.7, ,24, ,-4.4, , 92, , 7, ,100, , , ,30.09, , , , , ,30.40, ,AA, , , ,30.27, 

然后我创建了下表：

CREATE EXTERNAL TABLE weather(WBAN STRING, `Date` STRING, Time STRING, StationType INT, SkyCondition STRING, SkyConditionFlag STRING, Visibility INT, VisibilityFlag STRING, WeatherType STRING, WeatherTypeFlag STRING, DryBulbFarenheit INT, DryBulbFarenheitFlag STRING, DryBulbCelsius DECIMAL, DryBulbCelsiusFlag INT, WetBulbFarenheit INT, WetBulbFarenheitFlag INT, WetBulbCelsius DECIMAL, WetBulbCelsiusFlag INT, DewPointFarenheit INT, DewPointFarenheitFlag INT, DewPointCelsius DECIMAL, DewPointCelsiusFlag INT, RelativeHumidity INT, RelativeHumidityFlag INT, WindSpeed INT, WindSpeedFlag INT, WindDirection INT, WindDirectionFlag INT, ValueForWindCharacter INT, ValueForWindCharacterFlag INT, StationPressure DECIMAL, StationPressureFlag INT, PressureTendency INT, PressureTendencyFlag INT, PressureChange INT, PressureChangeFlag INT, SeaLevelPressure DECIMAL, SeaLevelPressureFlag INT, RecordType STRING, RecordTypeFlag STRING, HourlyPrecip DECIMAL, HourlyPrecipFlag INT, Altimeter DECIMAL, AltimeterFlag INT) 
    COMMENT 'Our weather table in HIVE!' 
    ROW FORMAT DELIMITED FIELDS TERMINATED BY ','
     LINES TERMINATED BY '\n' 
     LOCATION '/data/Weather';

现在，如果我尝试一个简单的查询，如下所示：

hive> select * from weather limit 10;

WBAN    Date    Time    NULL    SkyCondition    SkyConditionFlag    NULL    VisibilityFlag  WeatherType WeatherTypeFlag NULL    DryBulbFarenheitFlag    NULL    NULL    NULL    NULL    NULL    NULL    NULL    NULL    NULL    NULL    NULL    NULL    NULL    NULL    NULL    NULL    NULLNULL    NULL    NULL    NULL    NULL    NULL    NULL    NULL    NULL    RecordType  RecordTypeFlag  NULL    NULL    NULL    NULL
00102   20150101    0001    0   OVC043      10              27      -3  NULL    26  NULL    -3  NULL25  NULL    -4  NULL    NULL    NULL    NULL    NULL    0   NULL    NULL    NULL    30  NULL    NULL    NULL    NULL    NULL    30  NULL    AA      NULL    NULL    30  NULL
00102   20150101    0101    0   OVC045      10              27      -3  NULL    26  NULL    -3  NULL25  NULL    -4  NULL    NULL    NULL    NULL    NULL    80  NULL    NULL    NULL    30  NULL    NULL    NULL    NULL    NULL    30  NULL    AA      NULL    NULL    30  NULL
00102   20150101    0201    0   OVC047      10  

hive> select Visibility from weather limit 10;

我会得到正确的结果，但列标题/名称为空！！！

为什么列名称/标题为空？！

Answer 1

有趣的问题，我花了一分钟才意识到这是怎么回事，但有了对蜂巢的正确认识，它实际上是显而易见的！

1. 这里要注意的第一件事是，空值出现在不属于String类型的列中。
2. 需要注意的第二件事是，hive（例如，与beeline不同）通常不会在所选内容上方打印列标题。

所以，把1和2放在一起：

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