Re: Performing antijoin in postgres

["Heikki Linnakangas" <heikki(at)enterprisedb(dot)com>]

Suresh_ wrote:
> I want to add an antijoin operator to PostgreSql.  Basically I want to store
> the result (tupletableslot) of one join and then compare it with
> another..How do I store these results  and how do I compare them ?

I would suggest implementing it at a higher level, rewriting a query
like "A ANTIJOIN B" to "A EXCEPT (A JOIN B)". That allows the planner to
use whatever methods it has to perform the EXCEPT and the JOIN
operations. At the moment there's only one method: sort the inputs and
do a merge, but it's conceivable that you could implement EXCEPT using
hashing, for example.

-- 
  Heikki Linnakangas
  EnterpriseDB   http://www.enterprisedb.com