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https://issues.apache.org/jira/browse/PIG-1069?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Yan Zhou updated PIG-1069:
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Status: Patch Available (was: Open)
> [zebra] Order Preserving Sorted Table Union
> -------------------------------------------
>
> Key: PIG-1069
> URL: https://issues.apache.org/jira/browse/PIG-1069
> Project: Pig
> Issue Type: New Feature
> Affects Versions: 0.6.0
> Reporter: Yan Zhou
> Assignee: Yan Zhou
> Attachments: OrderPreservingSortedTableUnion_svn.patch
>
>
> The output schema will adopt a "schema union" semantics, namely, if an output
> column only appears in one component table, the result rows will have the
> values of the column if the rows are from that component table and null
> otherwise; on the other hand, if an output column appears in multiple
> component tables, the types of the column in all the component tables must be
> identical. Otherwise, an exception will be thrown. The result rows will have
> the values of the column if the rows are from the component tables that have
> the column themselves, or null if otherwise.
> The order preserving sort-unioned results could be further indexed by the
> component tables if the projection contains column(s) named "source_table".
> If so specified, the component table index will be output at the position(s)
> as specified in the projection list. If the underlying table is not a union
> of sorted tables, use of the special column name in projection will cause an
> exception thrown.
> If an attempt is made to create a table of a column named "source_table", an
> excpetion will be thrown as the name is reserved by zebra for the virtual
> name.
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