Re: Is this a bug, or is it just me?

Josh Berkus wrote:
> Tom et al.
>
> Discovered this quirk in foriegn keys:
>
> In the preliminary version of a database, I added foriegn
> key constraints to a number of tables, linking them to a
> column in a shared reference table (status.status) that was
> only one-half of a composite primary key (and thus the
> values were not unique).  When I tried to delete a row
> containing a "2" in the status column from the status
> relation, I received a Foreign Key violation error event
> though there were other "2"'s in the table still present.
>
> So ... is this a bug in forign key implementation, or just
> my fault for keying off a non-unique value?
>
> And, if the latter, is there a way I can construct a foreign
> key constraint that keys onto a view or query?
   The referenced columns of a foreign key constraint shall have   a unique constraint. That's how it is in the SQL
specs.  So   it  is a bug that the system let's you specify the constraint   at all. I think Stephan fixed it for 7.1.
 
   OTOH Postgres  doesn't  (and  shouldn't)  enforce  it  after,   because  if  it  would,  you couldn't drop/create a
corrupted  index.
 
   And no, you can't actually reference to a  view  or  anything   else  than a table. That is, because the system
wouldn'tknow   how to check for the DELETE/UPDATE cases on the  base  tables   building  the  view  if  the  removal
ofa key would violate   existing references.
 
   For such custom setups,  we  have  procedural  languages  and   triggers.


Jan

--

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