Re: Foreign Keys
От | Ben |
---|---|
Тема | Re: Foreign Keys |
Дата | |
Msg-id | Pine.LNX.4.44.0311211246180.7403-100000@localhost.localdomain обсуждение исходный текст |
Ответ на | Foreign Keys ("Thomas LeBlanc" <thomasatiem@hotmail.com>) |
Список | pgsql-general |
My understanding of forign keys is that the constraint is only checked when the values are non-null. I'm not aware of any way to say "keep the value non-null unless there is a null in the column referenced." On Fri, 21 Nov 2003, Thomas LeBlanc wrote: > I am able to enter a null in a foreign key field in one table(table2) > without the foreign key relationship (table1.t1_id) validating the value. > Why is this? > > Below are 2 table's scripts: > > create table table1 ( > t1_id VARCHAR(32) not null, > t1_desc VARCHAR(32) null, > constraint table1_pkey primary key (t1_id) ) ; > > > create table table2 ( > t2_id VARCHAR(32) not null, > t1_id VARCHAR(32) null, > t2_desc VARCHAR(32) null, > constraint table2_pkey primary key (t2_id) ) ; > > create index table2_t1_id > on table2 ( t1_id ) ; > > alter table table2 > add constraint table1_table2_t1_id_FK1 > foreign key ( t1_id ) > references table1 ( t1_id ) > ON DELETE RESTRICT ON UPDATE CASCADE ; > > _________________________________________________________________ > Is there a gadget-lover on your gift list? MSN Shopping has lined up some > good bets! http://shopping.msn.com > > > ---------------------------(end of broadcast)--------------------------- > TIP 7: don't forget to increase your free space map settings >
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