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From "Pala M Muthaia (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-6131) New columns after table alter result in null values despite data
Date Fri, 11 Apr 2014 19:24:18 GMT

    [ https://issues.apache.org/jira/browse/HIVE-6131?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13967001#comment-13967001
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Pala M Muthaia commented on HIVE-6131:
--------------------------------------

You are right, types of existing columns may change so partition schema may never be same
as table schema, so cannot pick one or the other. 

Let's say we support add columns DDL at partition level. What can be allowed? Can users add
arbitrarily different columns compared to table, or should they only add columns that are
present in table level, but are missing at partition level, in the same order? 

e.g: Initial schema: Table t (A, B, C, D), Partition p (A', B'). Can users only execute 'Alter
table t partition (p) add columns C,D'? Or can they do something else also 'alter table t
partition (p) add columns E, F, G'? 

If it is only the former, then we still can do the same programmatically, by 'merging' the
partition and table schema at runtime. However, if the table schema itself can be wildly different
compared to partition schema, then yes, DDL is the only option, and users have to manage it
themselves.

> New columns after table alter result in null values despite data
> ----------------------------------------------------------------
>
>                 Key: HIVE-6131
>                 URL: https://issues.apache.org/jira/browse/HIVE-6131
>             Project: Hive
>          Issue Type: Bug
>    Affects Versions: 0.11.0, 0.12.0, 0.13.0
>            Reporter: James Vaughan
>            Priority: Minor
>         Attachments: HIVE-6131.1.patch
>
>
> Hi folks,
> I found and verified a bug on our CDH 4.0.3 install of Hive when adding columns to tables
with Partitions using 'REPLACE COLUMNS'.  I dug through the Jira a little bit and didn't see
anything for it so hopefully this isn't just noise on the radar.
> Basically, when you alter a table with partitions and then reupload data to that partition,
it doesn't seem to recognize the extra data that actually exists in HDFS- as in, returns NULL
values on the new column despite having the data and recognizing the new column in the metadata.
> Here's some steps to reproduce using a basic table:
> 1.  Run this hive command:  CREATE TABLE jvaughan_test (col1 string) partitioned by (day
string);
> 2.  Create a simple file on the system with a couple of entries, something like "hi"
and "hi2" separated by newlines.
> 3.  Run this hive command, pointing it at the file:  LOAD DATA LOCAL INPATH '<FILEDIR>'
OVERWRITE INTO TABLE jvaughan_test PARTITION (day = '2014-01-02');
> 4.  Confirm the data with:  SELECT * FROM jvaughan_test WHERE day = '2014-01-02';
> 5.  Alter the column definitions:  ALTER TABLE jvaughan_test REPLACE COLUMNS (col1 string,
col2 string);
> 6.  Edit your file and add a second column using the default separator (ctrl+v, then
ctrl+a in Vim) and add two more entries, such as "hi3" on the first row and "hi4" on the second
> 7.  Run step 3 again
> 8.  Check the data again like in step 4
> For me, this is the results that get returned:
> hive> select * from jvaughan_test where day = '2014-01-01';
> OK
> hi	NULL	2014-01-02
> hi2	NULL	2014-01-02
> This is despite the fact that there is data in the file stored by the partition in HDFS.
> Let me know if you need any other information.  The only workaround for me currently
is to drop partitions for any I'm replacing data in and THEN reupload the new data file.
> Thanks,
> -James



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