Yan Zhou updated PIG-1069:

    Attachment: OrderPreservingSortedTableUnion_svn.patch

> [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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