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From Marc Harris <mhar...@jumptap.com>
Subject Re: "joining" more than two tables
Date Sun, 02 Mar 2008 21:31:46 GMT
Bump. I will not bump this again. Promise.
- Marc

On Mon, 2008-02-25 at 21:09 -0500, Marc Harris wrote:

> While there is no join in hbase, it is fairly easy to create a map
> reduce job that has the effect of scanning through two joined tables.
> However, I have not been able to figure out how to join three tables in
> this way. Is there a way to do this that I have missed?
> 
> Take the common teaching example of the teacher / student / class
> database.
> - A map reduce job that uses teachers with all their associated classes
> can be done by a mapper that outputs the teacher key from the teacher
> and class tables. 
> - A map reduce job that uses students with all their associated classes
> can be done by a mapper that outputs the student key from the student
> and class tables.
> - How can one create a map reduce job that uses teachers with all their
> associated students?
> 
> The only way I could think of was two jobs: one that creates a
> completely denormalized hbase table that combines the teacher and course
> tables, and a second that "joins" the interim table with the student
> table. This seems very space inefficient though. It basically requires a
> doubling of data storage. Any thoughts?
> 
> - Marc
> 

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