Order Preserving Sorted Table Union
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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
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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