hive-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Namit Jain <nj...@facebook.com>
Subject RE: How is Union All optimized in Hive
Date Wed, 25 Aug 2010 16:44:31 GMT
Yes, it is optimized by hive. There will be only 1 mr job, even if the columns selected were
different.


-namit

________________________________________
From: Neil Xu [neil.xuxf@gmail.com]
Sent: Wednesday, August 25, 2010 2:40 AM
To: hive-user@hadoop.apache.org
Subject: How is Union All optimized in Hive

I tried a query like below, same table, same column and different conditions, only one MR
job generated,  is it optimized by Hive itself? and is the' table_1' only scanned once? who
can give some details, thanks!

select a, b, c from table_1 where ...
union all
select a, b, c from table_1 where ...
union all
select a, b, c from table_1 where ...

Chocobo

Mime
View raw message