Обсуждение: two tables - foreign keys referring to each other...]

Chris,

> ..or generally: how do you create two crosslinked foreign keyed tables?
> 
> hopefully an easy problem for the real professionals!
No.  The problem is:  Why would you want to create two crosslinked
foriegn-keyed tables?  As an experienced SQL professional, this seems
like a recipe for instant disaster to me.
The purpose of a foriegn key is to enforce a parent-->child or data
table<--reference list relationships, to prevent incomplete or erroneous
records from being added.  This requires the foriegn key relationship to
be one-way.
In fact, if you built your two-way foriegn keys (using ALTER TABLE), I
think you might find that you can't add any records to either table. 
Certainly you won't be able to delete any.  I once had an experience
with a complex legacy data structure where I accidentally set up a
circular foriegn key relationship (among 5 tables), and I had to
re-build the database from scripts to fix it.
If you're looking to set up a many-to-many relationship, then what you
want is a linking table.  However, I highly advise you to pick up a
primer on database design (such as "Database Design for Mere Mortals")
before proceeding any further, or you'll end up spending the next year
paying for what you don't understand now.
                -Josh Berkus
-- 
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Josh Berkus <josh@agliodbs.com> wrote:
>In fact, if you built your two-way foriegn keys (using ALTER TABLE), I
>think you might find that you can't add any records to either table.
>Certainly you won't be able to delete any.

It can be done: use DEFERRABLE foreign key constraints (see
http://www.postgresql.org/docs/aw_pgsql_book/node161.html)

Ray
-- 
Personally, I guess I'd favor a sort of modified form of medieval justice.
The idea is that you throw the lawyers for both parties into a pond. The
person whose lawyer sinks would be declared the winner.       Rob Kleinschmidt