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From "Jason Dere (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-8448) Union All might not work due to the type conversion issue
Date Wed, 15 Oct 2014 21:39:34 GMT

    [ https://issues.apache.org/jira/browse/HIVE-8448?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14172996#comment-14172996
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Jason Dere commented on HIVE-8448:
----------------------------------

Don't know much about the history why there was getCommonClass/ForComparison/ForUnion.  Looks
like getCommonClassForUnionAll() was added in HIVE-2901, and getCommonClassForComparison()
added in HIVE-608. Might be possible to merge them all, but they each have some slight differences
which may change existing behavior.
I think the changes look good.

> Union All might not work due to the type conversion issue
> ---------------------------------------------------------
>
>                 Key: HIVE-8448
>                 URL: https://issues.apache.org/jira/browse/HIVE-8448
>             Project: Hive
>          Issue Type: Bug
>    Affects Versions: 0.13.1
>            Reporter: Chaoyu Tang
>            Assignee: Yongzhi Chen
>            Priority: Minor
>         Attachments: HIVE-8448.4.patch
>
>
> create table t1 (val date);
> insert overwrite table t1 select '2014-10-10' from src limit 1;
> create table t2 (val varchar(10));
> insert overwrite table t2 select '2014-10-10' from src limit 1; 
> ==
> Query:
> select t.val from
> (select val from t1
> union all
> select val from t1
> union all
> select val from t2
> union all
> select val from t1) t;
> ==
> Will throw exception: 
> {code}
> Caused by: org.apache.hadoop.hive.ql.metadata.HiveException: Incompatible types for union
operator
> 	at org.apache.hadoop.hive.ql.exec.UnionOperator.initializeOp(UnionOperator.java:86)
> 	at org.apache.hadoop.hive.ql.exec.Operator.initialize(Operator.java:380)
> 	at org.apache.hadoop.hive.ql.exec.Operator.initialize(Operator.java:464)
> 	at org.apache.hadoop.hive.ql.exec.Operator.initializeChildren(Operator.java:420)
> 	at org.apache.hadoop.hive.ql.exec.SelectOperator.initializeOp(SelectOperator.java:65)
> 	at org.apache.hadoop.hive.ql.exec.Operator.initialize(Operator.java:380)
> 	at org.apache.hadoop.hive.ql.exec.Operator.initialize(Operator.java:464)
> 	at org.apache.hadoop.hive.ql.exec.Operator.initializeChildren(Operator.java:420)
> 	at org.apache.hadoop.hive.ql.exec.TableScanOperator.initializeOp(TableScanOperator.java:193)
> 	at org.apache.hadoop.hive.ql.exec.Operator.initialize(Operator.java:380)
> 	at org.apache.hadoop.hive.ql.exec.MapOperator.initializeOp(MapOperator.java:443)
> 	at org.apache.hadoop.hive.ql.exec.Operator.initialize(Operator.java:380)
> 	at org.apache.hadoop.hive.ql.exec.mr.ExecMapper.configure(ExecMapper.java:133)
> 	... 22 more
> {code}
> It was because at this query parse step, getCommonClassForUnionAll is used, but at execution
getCommonClass is used. They are not used consistently in union. The later one does not support
the implicit conversion from date to string, which is the problem cause.
> The change might be simple to fix this particular union issue but I noticed that there
are three versions of getCommonClass: getCommonClass, getCommonClassForComparison, getCommonClassForUnionAll,
and wonder if they need to be cleaned and refactored.



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