Will all nested columns be read in an ORC file?












0















Say I have a Hive query like so:



CREATE TABLE student (key string, name string, course struct<class_name:string, class_teacher:string>) 

STORED AS ORC;


Because of the ORC file format, this will create 5 different columns:



| key | name | course | course.class_name | course.class_teacher |


When attempting to read only the course.class_name column, will both subcolumns of course be read anyway, every time? As in, both course.class_name and course.class_teacher ? As far as I am aware, ORC file format allows Hive to load only the columns needed for the query. So what will it actually do?






hadoop hive bigdata hiveql orc







share|improve this question



























    0















    Say I have a Hive query like so:



    CREATE TABLE student (key string, name string, course struct<class_name:string, class_teacher:string>) 
    
STORED AS ORC;


    Because of the ORC file format, this will create 5 different columns:



    | key | name | course | course.class_name | course.class_teacher |


    When attempting to read only the course.class_name column, will both subcolumns of course be read anyway, every time? As in, both course.class_name and course.class_teacher ? As far as I am aware, ORC file format allows Hive to load only the columns needed for the query. So what will it actually do?






    hadoop hive bigdata hiveql orc







    share|improve this question

























      0












      0








      0








      Say I have a Hive query like so:



      CREATE TABLE student (key string, name string, course struct<class_name:string, class_teacher:string>) 
      
STORED AS ORC;


      Because of the ORC file format, this will create 5 different columns:



      | key | name | course | course.class_name | course.class_teacher |


      When attempting to read only the course.class_name column, will both subcolumns of course be read anyway, every time? As in, both course.class_name and course.class_teacher ? As far as I am aware, ORC file format allows Hive to load only the columns needed for the query. So what will it actually do?






      hadoop hive bigdata hiveql orc







      share|improve this question














      Say I have a Hive query like so:



      CREATE TABLE student (key string, name string, course struct<class_name:string, class_teacher:string>) 
      
STORED AS ORC;


      Because of the ORC file format, this will create 5 different columns:



      | key | name | course | course.class_name | course.class_teacher |


      When attempting to read only the course.class_name column, will both subcolumns of course be read anyway, every time? As in, both course.class_name and course.class_teacher ? As far as I am aware, ORC file format allows Hive to load only the columns needed for the query. So what will it actually do?






      hadoop hive bigdata hiveql orc




      hadoop hive bigdata hiveql orc






      share|improve this question













      share|improve this question











      share|improve this question




      share|improve this question










      asked Jan 1 at 19:19









      crystyxncrystyxn

      279726




      279726
























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          Your understanding is right. It will read the only column which is specified in the select query.

          If select query is : 



          Select course.class_name from student


          It will return only class_name.

          In case if you want to query all the columns for the struct, you can use following.



          select key, name, c.* from students 
          
   lateral view inline (array(course)) c





          share|improve this answer























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            1 Answer
            1






            active

            oldest

            votes









            active

            oldest

            votes






            active

            oldest

            votes









            2














            Your understanding is right. It will read the only column which is specified in the select query.

            If select query is : 



            Select course.class_name from student


            It will return only class_name.

            In case if you want to query all the columns for the struct, you can use following.



            select key, name, c.* from students 
            
   lateral view inline (array(course)) c





            share|improve this answer




























              2














              Your understanding is right. It will read the only column which is specified in the select query.

              If select query is : 



              Select course.class_name from student


              It will return only class_name.

              In case if you want to query all the columns for the struct, you can use following.



              select key, name, c.* from students 
              
   lateral view inline (array(course)) c





              share|improve this answer


























                2












                2








                2







                Your understanding is right. It will read the only column which is specified in the select query.

                If select query is : 



                Select course.class_name from student


                It will return only class_name.

                In case if you want to query all the columns for the struct, you can use following.



                select key, name, c.* from students 
                
   lateral view inline (array(course)) c





                share|improve this answer













                Your understanding is right. It will read the only column which is specified in the select query.

                If select query is : 



                Select course.class_name from student


                It will return only class_name.

                In case if you want to query all the columns for the struct, you can use following.



                select key, name, c.* from students 
                
   lateral view inline (array(course)) c






                share|improve this answer












                share|improve this answer



                share|improve this answer










                answered Jan 2 at 12:41









                Nishu TayalNishu Tayal

                12.6k73482




                12.6k73482
































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