From: Richard Huxton <dev@archonet.com>
To: Larry Rosenman <ler@lerctr.org>, pgsql-sql@postgresql.org
Subject: Re: weird(to me) request
Date: Thu, 25 Sep 2003 20:09:35 +0100
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On Thursday 25 September 2003 19:51, Larry Rosenman wrote:
> I have the following rows (in addition to others):
>
> acct_num text,
> master_acct_num text,
>
>
> These are in the same table.
>
> What I want to enforce is that if the master_acct_num field is NOT NULL (it
> can be NULL, and
> that's fine), that the value appears in some row as acct_num.  acct_num has
> a unique index on it, so that's fine.
>
> I'm not sure how to do this....

ALTER TABLE my_table ADD CONSTRAINT my_self_fk FOREIGN KEY (master_acct_num) 
REFERENCES my_table (acct_num);

It's really just a foreign-key to yourself
-- 
  Richard Huxton
  Archonet Ltd