Обсуждение: deleting the master but not the detail
hi I have one of those master-detail relationships here and I need to be able to delete the master but leave the details untouched But the delete command doesn't let me delete the master as long as there are details referencing it. ON DELETE RESTRICT | NO ACTION won't let me delete the master CASCADE | SET NULL | SET DEFAULT will modify the details Any idea ow to do it without the use of triggers? SQL Server is got the option "ON DELETE DO NOTHING" or something like that, that just oversees the deletion, but I didn't find it for postgres. _________________________________________________________________ P.D. Checa las nuevas fotos de mi Space http://home.services.spaces.live.com/
am Thu, dem 17.07.2008, um 11:11:00 -0500 mailte Ismael .... folgendes:
>
> hi
> I have one of those master-detail relationships here and I need to be able
> to delete the master but leave the details untouched
>
> But the delete command doesn't let me delete the master as long as
> there are details referencing it.
>
> ON DELETE RESTRICT | NO ACTION won't let me delete the master
> CASCADE | SET NULL | SET DEFAULT will modify the details
>
> Any idea ow to do it without the use of triggers?
DROP the constraint. For example:
test=# create table master (id serial primary key, m text);
NOTICE: CREATE TABLE will create implicit sequence "master_id_seq" for serial column "master.id"
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "master_pkey" for table "master"
CREATE TABLE
test=*# insert into master (m) values ('master1');
INSERT 0 1
test=*# insert into master (m) values ('master2');
INSERT 0 1
test=*# create table slave (id int references master, s text);
CREATE TABLE
test=*# insert into slave values (1, 'slave 1');
INSERT 0 1
test=*# insert into slave values (2, 'slave 2');
INSERT 0 1
test=*# \d slave
Tabelle »public.slave«
Spalte | Typ | Attribute
--------+---------+-----------
id | integer |
s | text |
Fremdschlüssel-Constraints:
»slave_id_fkey« FOREIGN KEY (id) REFERENCES master(id)
test=*# alter table slave drop constraint slave_id_fkey;
ALTER TABLE
test=*# drop table master;
DROP TABLE
test=*# select * from slave;
id | s
----+---------
1 | slave 1
2 | slave 2
(2 Zeilen)
test=*#
Hope that helps, Andreas
--
Andreas Kretschmer
Kontakt: Heynitz: 035242/47150, D1: 0160/7141639 (mehr: -> Header)
GnuPG-ID: 0x3FFF606C, privat 0x7F4584DA http://wwwkeys.de.pgp.net
On 17/07/2008 17:11, Ismael .... wrote: > ON DELETE RESTRICT | NO ACTION won't let me delete the master > CASCADE | SET NULL | SET DEFAULT will modify the details Can you just drop the constraint that's doing the referential integrity? Ray. ------------------------------------------------------------------ Raymond O'Donnell, Director of Music, Galway Cathedral, Ireland rod@iol.ie Galway Cathedral Recitals: http://www.galwaycathedral.org/recitals ------------------------------------------------------------------
So is there no other way to do it but to verify the integrity using triggers and drop the referential constraints? Because I *still* need to verify that NEW records in the details table direct to something that exists > >> ON DELETE RESTRICT | NO ACTION won't let me delete the master >> CASCADE | SET NULL | SET DEFAULT will modify the details > > Can you just drop the constraint that's doing the referential integrity? > > Ray. > > Then remove the referential integrity constraint, since it's obviously > incompatible with your business requirements. > > -Doug _________________________________________________________________ Plug&Play te trae en exclusiva los mejores conciertos de la red http://club.prodigymsn.com/
On Thu, Jul 17, 2008 at 12:11 PM, Ismael .... <ismaelpsp@hotmail.com> wrote: > > hi > I have one of those master-detail relationships here and I need to be able > to delete the master but leave the details untouched Then remove the referential integrity constraint, since it's obviously incompatible with your business requirements. -Doug
On Thu, Jul 17, 2008 at 10:52 AM, Douglas McNaught <doug@mcnaught.org> wrote: > On Thu, Jul 17, 2008 at 12:11 PM, Ismael .... <ismaelpsp@hotmail.com> wrote: >> >> hi >> I have one of those master-detail relationships here and I need to be able >> to delete the master but leave the details untouched > > Then remove the referential integrity constraint, since it's obviously > incompatible with your business requirements. Generally I'd agree, but it might be useful to set the child record referencing id field to NULL in this circumstance.
It seems like 3 vs 1 so you win :) I'll drop the constraint and verify the integrity of the new records manually tanks > > On Thu, Jul 17, 2008 at 10:52 AM, Douglas McNaught wrote: >> On Thu, Jul 17, 2008 at 12:11 PM, Ismael .... wrote: >>> >>> hi >>> I have one of those master-detail relationships here and I need to be able >>> to delete the master but leave the details untouched >> >> Then remove the referential integrity constraint, since it's obviously >> incompatible with your business requirements. > > Generally I'd agree, but it might be useful to set the child record > referencing id field to NULL in this circumstance. _________________________________________________________________ Tenemos lo que búscas…JUEGOS. http://club.prodigymsn.com/
>>>> hi >>>> I have one of those master-detail relationships here and I need to be able >>>> to delete the master but leave the details untouched when you create the table with an FK constraint, use the ON DELETE SET NULL option, or SET DEFAULT. And read the docs on "CREATE TABLE": http://www.postgresql.org/docs/8.3/static/sql-createtable.html >>> >>> Then remove the referential integrity constraint, since it's obviously >>> incompatible with your business requirements. Wrong. See above. Unless I misunderstand, then I apologize for the noise....
On Thu, 17 Jul 2008, Ismael .... wrote: > So is there no other way to do it but to verify the integrity using triggers > and drop the referential constraints? Well, you could do something using a before delete trigger on the referencing table that returns NULL to avoid the delete as well, but making it only prevent the deletions caused by the referential constraints might be difficult.
> >> So is there no other way to do it but to verify the integrity using triggers >> and drop the referential constraints? > > Well, you could do something using a before delete trigger on the > referencing table that returns NULL to avoid the delete as well, but > making it only prevent the deletions caused by the referential constraints > might be difficult. > That's right, It's easier to verify the existence of the master before inserting something in the details than controlling the way something gets deleted. After all, is only a PERFORM * FROM.... WHERE NEW..... IF NOT FOUND THEN RISE EXCEPTION 'that doesn't exists';... _________________________________________________________________ Plug&Play te trae en exclusiva los mejores conciertos de la red http://club.prodigymsn.com/