Re: Integrity violation when adding foreign key constraint

Unfortunately there is a bug in 7.0.x's alter table add constraint
that gets the column definitions wrong (I had misinterpreted the
ordering of arguments to the trigger).  I think I sent the patch
to someone over the mailing list so it should be in the archives.

On Mon, 26 Mar 2001, Daniel Hartmeier wrote:

> I hope somebody can help me with a question. I have two tables
>
>   CREATE TABLE sk (
>     fnr INTEGER,
>     knr SMALLINT,
>      [...]
>     CONSTRAINT sk_pk_fnr_knr PRIMARY KEY ( fnr, knr )
>   );
>
>   CREATE TABLE sg (
>     fnr INTEGER,
>     knr SMALLINT,
>     gpc CHAR(1),
>      [...]
>     CONSTRAINT sg_pk_fnr_knr_gpc PRIMARY KEY ( fnr, knr, gpc )
>   );
>
> loaded with data. When I try to add a foreign key constraint with
>
>   ALTER TABLE sg ADD CONSTRAINT sg_fk_fnr_knr FOREIGN KEY ( fnr, knr )
>     REFERENCES sk;
>
> I get the error message
>
>   NOTICE:  ALTER TABLE ... ADD CONSTRAINT will create implicit trigger(s) for
>            FOREIGN KEY check(s)
>   ERROR:  <unnamed> referential integrity violation - key referenced from
>                     sg not found in sk
>
> But when I try to find the offending row(s) in sg with
>
>   SELECT * FROM sg WHERE NOT EXISTS ( SELECT * FROM sk WHERE
>     sk.fnr = sg.fnr AND sk.knr = sg.knr );
>
> I get nothing (0 rows).
>
> This is PostgreSQL 7.0.3 on BSD, and I ran vacuum analyze on both tables
> first.
>
> Am I doing something wrong, or what might be a reason for what looks
> like a contradiction to me? Foreign keys on multiple columns work like
> this, don't they?
>
> Kind regards,
> Daniel
>
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