Re: Setting a FK to look at only selected rows in the 'look-up' table...
| От | Greg Cocks |
|---|---|
| Тема | Re: Setting a FK to look at only selected rows in the 'look-up' table... |
| Дата | |
| Msg-id | 66F6CF82BF58CE4DB4285BE816B297E83BA9B6@tribble.SMStoller.com обсуждение исходный текст |
| Ответ на | Re: Setting a FK to look at only selected rows in the 'look-up' table... ("Sean Davis" <sdavis2@mail.nih.gov>) |
| Список | pgsql-novice |
Sean, Tom, Others…
Two column FK – perfect! I have used them elsewhere, not sure why I did not think of them in this instance!
“Thanks list…” J
From: Sean Davis [mailto:sdavis2@mail.nih.gov]
Sent: Friday, December 28, 2007 8:29 PM
To: Tom Lane
Cc: Greg Cocks; PostgreSQL List - Novice
Subject: Re: [NOVICE] Setting a FK to look at only selected rows in the 'look-up' table...
On Dec 28, 2007 10:11 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
"Sean Davis" <sdavis2@mail.nih.gov> writes:
> On Dec 28, 2007 7:01 PM, Greg Cocks <gcocks@stoller.com > wrote:
>> I would like to restrict the foreign key for d_borehole.depth_unit to be
>> only those values in r_unit.unit_id where r_unit.unit_length = 'length' (
>> i.e., so that only applicable 'length' units can be utilized for the
>> depths (feet, metres, inches, etc))
> This cannot be done with foreign keys I don't think.
Maybe I missed something, but couldn't a two-column foreign key
constraint on (value, unit) be made to serve the purpose?
Yep. If he modifies his schema somewhat to include the extra column in the first table.
Sean
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