title: Is there a way to fill the newly added columns with data in an already existing partition?
body: <p>I am working with Hive's dynamic partitions, and I am having an issue with a column not being populated with data unless a new partition is added. I have created a small demo example to demonstrate.</p>
  
  <pre>
  1. create table vegetables (name string, count bigint) partitioned by (year int, month int, day int);
  2. create external  table dataForVeg (name string, count bigint, weight string, year int, month int, day int) row format delimited fields terminated by ' ';
  3. load data1 into dataforveg 
  4. set hive.exec.dynamic.partition.mode=nonstrict;
  5. insert into table vegetables  partition(year, month, day) select name, count, year, month, day from dataforveg;
  
  6. hive> select * from vegetables where day='5';
  tomato  5       2013    11      5
  cabbage 3       2013    11      5
  
  7. hive> alter table  vegetables add columns(weight double);
  8. hive> describe vegetables ;
  name    string
  count   bigint
  weight  double
  year    int
  month   int
  day     int
  
  9. hive> select * from vegetables where day='5';
  tomato  5       NULL    2013    11      5
  cabbage 3       NULL    2013    11      5
  
  hive> select * from vegetables where day='4';
  potato  2       NULL    2013    11      4
  
  10. load overwrite data2 into dataforveg 
  11. hive> select * from dataforveg;
  carrot  10      5       2013    11      5
  pepper  15      2       2013    11      5
  
  12. hive> select *  from vegetables where day='5';
  tomato  5       NULL    2013    11      5
  cabbage 3       NULL    2013    11      5
  carrot  10      NULL    2013    11      5
  pepper  15      NULL    2013    11      5
  
  13. load overwrite data3 into dataforveg 
  hive> select * from dataforveg;
  beet      4       1       2013    11      6
  broccoli  3       1       2013    11      6
  
  14. hive> select *  from vegetables;
  potato  2       NULL    2013    11      4
  tomato  5       NULL    2013    11      5
  cabbage 3       NULL    2013    11      5
  carrot  10      NULL    2013    11      5
  pepper  15      NULL    2013    11      5
  beet    4       1.0     2013    11      6
  broccoli 3       1.0     2013    11      6
  </pre>
  
  <p>As you can see from the example, data is being updated when you add a new partition.
  Question: is there a way to refresh the value of a new field 'weight' for carrot and pepper in step 12? 
  In other words, is there a way to fill the newly added columns with data in an already existing partition?</p>