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https://issues.apache.org/jira/browse/PIG-1461?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12895383#action_12895383
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Olga Natkovich commented on PIG-1461:
-------------------------------------
The patch looks good. A couple of comments:
(1) Looks like there is a type in the code that loads data for testing:
w.println("5\tdef\t3\t{(2,a),(2,b)}]"); - contains an extra "]" at the end
(2) This is not related to the patch but to the documentation above. Please,
add info that UNION supports 2 or more inputs.
(3) In mergeSchemasByAlias, I think it is safer to make copy of the schema
rather than just assigning it for the corner case of 1 schema.
(4) Need to add a comment about inner bag schema to
mergeFieldSchemaFirstLevelSameAlias
(5) General comment on schema merging - we have completely different code path
for posiiton vs. alias based merge. I am worried that we will have subtly
different semantics either now or later.
> 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
>
> Attachments: PIG-1461.1.patch, PIG-1461.patch
>
>
> 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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