Re: Converting multiple joins into a single multi-way join

[Zheng Shao]

See ql/src/test/queries/clientpositive/uniquejoin.q


FROM UNIQUEJOIN PRESERVE T1 a (a.key), PRESERVE T2 b (b.key), PRESERVE
T3 c (c.key)
SELECT a.key, b.key, c.key;

FROM UNIQUEJOIN T1 a (a.key), T2 b (b.key), T3 c (c.key)
SELECT a.key, b.key, c.key;

FROM UNIQUEJOIN T1 a (a.key), T2 b (b.key-1), T3 c (c.key)
SELECT a.key, b.key, c.key;

FROM UNIQUEJOIN PRESERVE T1 a (a.key, a.val), PRESERVE T2 b (b.key,
b.val), PRESERVE T3 c (c.key, c.val)
SELECT a.key, a.val, b.key, b.val, c.key, c.val;

FROM UNIQUEJOIN PRESERVE T1 a (a.key), T2 b (b.key), PRESERVE T3 c (c.key)
SELECT a.key, b.key, c.key;

FROM UNIQUEJOIN PRESERVE T1 a (a.key), T2 b(b.key)
SELECT a.key, b.key;


Zheng

On Wed, Feb 3, 2010 at 2:07 AM, bharath v
<bharathvissapragada1...@gmail.com> wrote:
>
> Hi ,
>
> Can anyone give me an example in which there is an optimization of
> "Converting multiple joins into a single multi-way join" .. i.e., reducing
> the number of map-reduce jobs .
> I read this from hive's design document but I couldn't find any example .
> Can anyone point me to the same??
>
> Kindly help,
>
> Thanks
>



-- 
Yours,
Zheng