[Hadoop Wiki] Update of "Hive/PartitionedViews" by JohnSichi

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The "Hive/PartitionedViews" page has been changed by JohnSichi.
http://wiki.apache.org/hadoop/Hive/PartitionedViews

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New page:
This is a followup to [[Hive/ViewDev]] for adding partition-awareness to views.

= Use Cases =

* An administrator wants to create a set of views as a table/column renaming layer on top of an existing set of base tables, without disturbing the ETL processes which load those tables.  To read-only users, the views should behave exactly the same as the underlying tables in every way.  Among other things, this means users should be able to browse available partitions.
* A base table is partitioned on columns (ds,hr) for date and hour.  Besides this fine-grained partitioning, users would also like to see a virtual table of coarse-grained (date-only) partitioning in which the partition for a given date only appears once all of the hour-level partitions of that day have been fully loaded.
* A view is defined on a complex join+union+aggregation of a number of underlying base tables and other views, all of which are themselves partitioned.  The top-level view should also be partitioned accordingly, with a new partition not appearing until corresponding partitions have been loaded for all of the underlying tables.