Обсуждение: Problem Deleting Referenced records
Hi, I have two tables , A and B where table B has a foreign key constraint to table A. I want to delete all records in table A that are older than a certain date that are not referenced by table B. When I use a DELETE FROM the entire transaction fails as soon as a referential integrity violation is detected. Is that the normal behavior? Is there a way to allow the deletion to complete but skipping all those records that are referenced ? Thanks in advance for any help. Alex
On Mon, Nov 10, 2003 at 14:31:00 +0900, Alex <alex@meerkatsoft.com> wrote: > Hi, > I have two tables , A and B where table B has a foreign key constraint > to table A. > > I want to delete all records in table A that are older than a certain > date that are not referenced by table B. > > When I use a DELETE FROM the entire transaction fails as soon as a > referential integrity violation is detected. > > Is that the normal behavior? Is there a way to allow the deletion to > complete but skipping all those records that are referenced ? I think you want to do something like: delete from A where A.stamp < current_date - '1 month' and not exists (select 1 from B where B.Aid = A.id); It is also possible to join A and B on the delete command using a nonstandard syntax, but not exists should be about as fast.
Bruno, thanks. I actually did it that way but having to join two tables each 1-2 million records makes this process rather time consuming. I was hoping that the ON DELETE options in the constraint could handle that. It seems to be a bit odd that if I want to delete 100 records that are not related to each other, and one record deletion fails that then the entire delete process fails. ... but I guess there is nothing I can do about. Alex Bruno Wolff III wrote: >On Mon, Nov 10, 2003 at 14:31:00 +0900, > Alex <alex@meerkatsoft.com> wrote: > > >>Hi, >>I have two tables , A and B where table B has a foreign key constraint >>to table A. >> >>I want to delete all records in table A that are older than a certain >>date that are not referenced by table B. >> >>When I use a DELETE FROM the entire transaction fails as soon as a >>referential integrity violation is detected. >> >>Is that the normal behavior? Is there a way to allow the deletion to >>complete but skipping all those records that are referenced ? >> >> > >I think you want to do something like: > >delete from A where A.stamp < current_date - '1 month' and > not exists (select 1 from B where B.Aid = A.id); > >It is also possible to join A and B on the delete command using a nonstandard >syntax, but not exists should be about as fast. > >---------------------------(end of broadcast)--------------------------- >TIP 5: Have you checked our extensive FAQ? > > http://www.postgresql.org/docs/faqs/FAQ.html > > > >
On Mon, Nov 10, 2003 at 16:20:21 +0900, Alex <alex@meerkatsoft.com> wrote: > Bruno, > thanks. I actually did it that way but having to join two tables each > 1-2 million records makes this process rather time consuming. > I was hoping that the ON DELETE options in the constraint could handle > that. If only a small number of the 1-2 million records have old dates, than the where not exists method might be faster. An index scan could be used to find the records with old dates and then for each record an index lookup could be done in table B to see if it should really be deleted. > > It seems to be a bit odd that if I want to delete 100 records that are > not related to each other, and one record deletion fails that then the > entire delete process fails. You can delete each record in its own transaction if you want that behavior.
Bruno, I am not sure why but the whole delete proces with the where not exists method took 3hrs, rather long I would say. Table A had 2.5mil records Table B had about 30k records In addition Table C with about 2 mil records referenced a referenced A (same key as B) In both A and B about 150k records where deleted... but the process took more than 3 hrs. Its pretty long I would say. I noticed in the past that if I had multiple foreign keys, referencing different tables like TableA <-- TableB <-- TableC then deletes are really slow... sometimes in the area of one delete per second. Never really figured out why. (And yes I did run a Vacuum or Vacuum analyze on the DB or Tables). Alex Bruno Wolff III wrote: >On Mon, Nov 10, 2003 at 16:20:21 +0900, > Alex <alex@meerkatsoft.com> wrote: > > >>Bruno, >>thanks. I actually did it that way but having to join two tables each >>1-2 million records makes this process rather time consuming. >>I was hoping that the ON DELETE options in the constraint could handle >>that. >> >> > >If only a small number of the 1-2 million records have old dates, than the >where not exists method might be faster. An index scan could be used >to find the records with old dates and then for each record an index >lookup could be done in table B to see if it should really be deleted. > > > >>It seems to be a bit odd that if I want to delete 100 records that are >>not related to each other, and one record deletion fails that then the >>entire delete process fails. >> >> > >You can delete each record in its own transaction if you want that >behavior. > >---------------------------(end of broadcast)--------------------------- >TIP 1: subscribe and unsubscribe commands go to majordomo@postgresql.org > > > >
On Wed, Nov 12, 2003 at 00:08:02 +0900, Alex <alex@meerkatsoft.com> wrote: > Bruno, > I am not sure why but the whole delete proces with the where not exists > method took 3hrs, rather long I would say. > > Table A had 2.5mil records > Table B had about 30k records > > In addition Table C with about 2 mil records referenced a referenced A > (same key as B) > In both A and B about 150k records where deleted... but the process took > more than 3 hrs. > > Its pretty long I would say. I noticed in the past that if I had > multiple foreign keys, referencing different tables like TableA <-- > TableB <-- TableC then deletes are really slow... sometimes in the area > of one delete per second. Never really figured out why. (And yes I did > run a Vacuum or Vacuum analyze on the DB > or Tables). If you do a lot of deleting of rows in referenced tables, then you probably want to create indexes in the referencing tables for the key. This will allow for quicker checks by the referential integrity checking triggers.