Thread: fk problems with 0..n relations
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.
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? __________________________________________ Yahoo! DSL Something to write home about. Just $16.99/mo. or less. dsl.yahoo.com