Thread: Performing antijoin in postgres
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 ? -- View this message in context: http://www.nabble.com/Performing-antijoin-in-postgres-tf4358905.html#a12422596 Sent from the PostgreSQL - hackers mailing list archive at Nabble.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
"Suresh_" <suiyengar@yahoo.com> writes: > I want to add an antijoin operator to PostgreSql. I think you can already do what you want like this: SELECT * FROM A FULL OUTER JOIN B ON (x=y)WHERE x IS NULL OR y IS NULL So for example: postgres=# select * from a;i ---12 (2 rows) postgres=# select * from b;i ---23 (2 rows) postgres=# select * from a full outer join b on (a.i=b.i) where a.i is null or b.i is null;i | i ---+---1 | | 3 (2 rows) -- Gregory Stark EnterpriseDB http://www.enterprisedb.com
Thanks for the reply. I can do this at the higher level; but this antijoin thing is a small part of a bigger project. So I want to do it internally in one of the joins. Does anyone have experience in storing tupleslpts and comparing them ?? Gregory Stark wrote: > > "Suresh_" <suiyengar@yahoo.com> writes: > >> I want to add an antijoin operator to PostgreSql. > > I think you can already do what you want like this: > > SELECT * > FROM A FULL OUTER JOIN B ON (x=y) > WHERE x IS NULL > OR y IS NULL > > So for example: > > postgres=# select * from a; > i > --- > 1 > 2 > (2 rows) > > postgres=# select * from b; > i > --- > 2 > 3 > (2 rows) > > postgres=# select * from a full outer join b on (a.i=b.i) where a.i is > null or b.i is null; > i | i > ---+--- > 1 | > | 3 > (2 rows) > > -- > Gregory Stark > EnterpriseDB http://www.enterprisedb.com > > ---------------------------(end of broadcast)--------------------------- > TIP 6: explain analyze is your friend > > -- View this message in context: http://www.nabble.com/Performing-antijoin-in-postgres-tf4358905.html#a12425655 Sent from the PostgreSQL - hackers mailing list archive at Nabble.com.