From: Leif Biberg Kristensen <leif@solumslekt.org>
To: pgsql-sql@postgresql.org
Subject: DDL problems: Referential issue?
Date: Wed, 4 Nov 2009 19:03:36 +0100
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PostgreSQL 8.3.8 on Gentoo Linux.

I've got a junction table:

CREATE TABLE participants (
    person_fk INTEGER REFERENCES persons (person_id),
    event_fk INTEGER REFERENCES events (event_id) ON DELETE CASCADE,
    sort_order INTEGER NOT NULL DEFAULT 1,
    is_principal BOOLEAN NOT NULL DEFAULT TRUE,
    PRIMARY KEY (person_fk, event_fk)
);
CREATE INDEX event_key ON participants (event_fk);
CREATE INDEX person_key ON participants (person_fk);

Now I want to add some text to a few participants, but as this will probably 
only be for a few per cent, I try to create an extra table like this:

pgslekt=> CREATE TABLE participant_notes (
pgslekt(>     person_fk   INTEGER NOT NULL REFERENCES participants 
(person_fk),
pgslekt(>     event_fk    INTEGER NOT NULL REFERENCES participants (event_fk) 
ON DELETE CASCADE,
pgslekt(>     part_note   TEXT,
pgslekt(>     PRIMARY KEY (person_fk, event_fk)
pgslekt(> );
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index 
"participant_notes_pkey" for table "participant_notes"
ERROR:  there is no unique constraint matching given keys for referenced table 
"participants"

I fail to see what is the problem. I even tried to add a unique constraint to 
participants:

pgslekt=> alter table participants add constraint unique_person_event unique 
(person_fk, event_fk);
NOTICE:  ALTER TABLE / ADD UNIQUE will create implicit index 
"unique_person_event" for table "participants"
ALTER TABLE                                                                                               

But I still get the same error message as above.

This works fine, naturally:

pgslekt=> CREATE TABLE participant_notes (                            
pgslekt(>     person_fk   INTEGER NOT NULL references persons (person_id),
pgslekt(>     event_fk    INTEGER NOT NULL references events (event_id) ON 
DELETE CASCADE,
pgslekt(>     part_note   TEXT,                                                           
pgslekt(>     PRIMARY KEY (person_fk, event_fk)                                           
pgslekt(> );                                                                              
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index 
"participant_notes_pkey" for table "participant_notes"
CREATE TABLE                                                                                                         

However, I think that this table should reference participants, not the 
primary tables persons and events.
-- 
Leif Biberg Kristensen
http://solumslekt.org