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From "Yan Zhou (JIRA)" <j...@apache.org>
Subject [jira] Updated: (PIG-1069) [zebra] Order Preserving Sorted Table Union
Date Sat, 07 Nov 2009 14:21:32 GMT

     [ https://issues.apache.org/jira/browse/PIG-1069?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

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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