[Hadoop Wiki] Update of "Hive/LanguageManual/VirtualColumns" by HeYongqiang

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The "Hive/LanguageManual/VirtualColumns" page has been changed by HeYongqiang.
http://wiki.apache.org/hadoop/Hive/LanguageManual/VirtualColumns

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New page:
<<TableOfContents>>

== Virtual Columns ==

Right now hive can only support 2 simple virtual columns:


One is {{{INPUT__FILE__NAME}}}, which is the input file's name for a mapper task.


the other is {{{BLOCK__OFFSET__INSIDE__FILE}}}, which is the current global file position. 

For block compressed file, it is the current block's file offset, which is the current block's first byte's file offset.

=== Simple Examples ===

select {{{INPUT__FILE__NAME}}}, key, {{{BLOCK__OFFSET__INSIDE__FILE}}} from src;

select key, count({{{INPUT__FILE__NAME}}}) from src group by key order by key;

select * from src where {{{BLOCK__OFFSET__INSIDE__FILE}}} > 12000 order by key;