Обсуждение: fk problems with 0..n relations

On Mon, Dec 05, 2005 at 01:45:37 -0000,
  Luis Silva <lfs12@hotmail.com> wrote:
> I there, i'm having a problem. i have a table(1) that is connected with two multiple table (2 and 3). the problem is
thatthe table 1 might have one of the tables (2 or 3, or both). how can i make this relationship in sql. Resuming,
table1 as a 0..n relation with table 2 and 3. thanks in advance. 

Normally you just have tables 2 and 3 refer to table 1 and not the other way
around.

If you need to make sure that the entry in table 1 corresponds to at least
one entry in table 2 or table 3, then you can have table 1 refer to both
table 2 and table 3, but allow nulls. Then you use a constraint to make
sure at least one of the references is not null.

--- Luis Silva <lfs12@hotmail.com> wrote:

> I there, i'm having a problem. i have a table(1)
> that is connected with two multiple table (2 and 3).
> the problem is that the table 1 might have one of
> the tables (2 or 3, or both). how can i make this
> relationship in sql. Resuming, table 1 as a 0..n
> relation with table 2 and 3. thanks in advance.

Louis, i'm not sure i understand your question fully.
it would help if you post sample data (even if made
up).

in any case, someone mentioned that you could link
table 1 as follows:

table_1:
news_id
news

table_2:
image_id
image
fk_news_id

table_3
comment_id
comment
fk_news_id

if table 2 is linked to table 1, drop in news_id into
table_2.fk_news_id.

if table 3 is linked to table 1, drop in news_id into
table_3.fk_news_id.

drop in both if it is linked to both.

does this answer your question?



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