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https://issues.apache.org/jira/browse/HIVE-16050?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15886464#comment-15886464
 ] 

Gopal V commented on HIVE-16050:
--------------------------------

Yup, right at the top of the function.

{code}
    if (a.equals(b)) {
      return a;
    }
{code}

Without that equals at the top, the code will convert a union of 2 Dates  into 
a timestamp column.

Beyond that case, I'm extremely suspicious of all the .q changes in HIVE-14251, 
if they all represent a query which worked in 2.1.x and won't in 2.2.x branch.

> Regression: Union of null with non-null 
> ----------------------------------------
>
>                 Key: HIVE-16050
>                 URL: https://issues.apache.org/jira/browse/HIVE-16050
>             Project: Hive
>          Issue Type: Bug
>          Components: Query Planning
>    Affects Versions: 2.2.0
>            Reporter: Gopal V
>            Assignee: Gopal V
>             Fix For: 2.2.0
>
>         Attachments: HIVE-16050.1.patch
>
>
> {code}
> hive> select null as c1 union select 1 as c2;
>     FAILED: SemanticException Schema of both sides of union should match: 
> Column c1 is of type void on first table and type int on second table. Cannot 
> tell the position of null AST.
> {code}
> This looks related to HIVE-14251 which removed certain cases from the UNION 
> type coercion operations.



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