[jira] Commented: (PIG-1461) support union operation that merges based on column names

["Thejas M Nair (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/PIG-1461?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12892892#action_12892892 ] 

Thejas M Nair commented on PIG-1461:
------------------------------------

The syntax - " union ... using 'merge' " introduces a new use of the " using '...' " clause. So far this clause has been used to indicate the implementation algorithm and it did not have any impact on the semantics. 
Instead a key word might be better if we are trying to avoid introducing another top level operator, similar to the case of outer joins -   eg - " union onschema L1, L2;"

More suggestions/opinions on the syntax for this feature are welcome.



> support union operation that merges based on column names
> ---------------------------------------------------------
>
>                 Key: PIG-1461
>                 URL: https://issues.apache.org/jira/browse/PIG-1461
>             Project: Pig
>          Issue Type: New Feature
>          Components: impl
>    Affects Versions: 0.8.0
>            Reporter: Thejas M Nair
>            Assignee: Thejas M Nair
>             Fix For: 0.8.0
>
>
> When the data has schema, it often makes sense to union on column names in schema rather than the position of the columns. 
> The behavior of existing union operator should remain backward compatible .
> This feature can be supported using either a new operator or extending union to support 'using' clause . I am thinking of having a new operator called either unionschema or merge . Does anybody have any other suggestions for the syntax ?
> example -
> L1 = load 'x' as (a,b);
> L2 = load 'y' as (b,c);
> U = unionschema L1, L2;
> describe U;
> U: {a:bytearray, b:byetarray, c:bytearray}

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