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https://issues.apache.org/jira/browse/HIVE-14251?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15385959#comment-15385959
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Chaoyu Tang commented on HIVE-14251:
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[~aihuaxu] Do you know why and under what situation the string could be
considered to be implicitly converted to double? I believe it breaks your case
because the date string could be converted to double. If we add a flag to
disable this implicit conversion generally in getCommonClassForUnionAll, will
it bring in possible backward type incompatibility in some queries with union
all for type string and double?
> Union All of different types resolves to incorrect data
> -------------------------------------------------------
>
> Key: HIVE-14251
> URL: https://issues.apache.org/jira/browse/HIVE-14251
> Project: Hive
> Issue Type: Bug
> Components: Query Planning
> Affects Versions: 2.0.0
> Reporter: Aihua Xu
> Assignee: Aihua Xu
> Attachments: HIVE-14251.1.patch
>
>
> create table src(c1 date, c2 int, c3 double);
> insert into src values ('2016-01-01',5,1.25);
> select * from
> (select c1 from src union all
> select c2 from src union all
> select c3 from src) t;
> It will return NULL for the c1 values. Seems the common data type is resolved
> to the last c3 which is double.
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