simple addition of constraints problem

On Tue, Jun 08, 2004 at 05:51:22PM -0400, Michelle Murrain wrote:

I'd like to make 'courseid' in this second table a foreign key,
referencing 'courseid' in the first table. So I did this command:

charter_dev2=# ALTER TABLE coursesevaluations ADD CONSTRAINT rc_ce
FOREIGN KEY (courseid) REFERENCES rcourseinfo (courseid);

And I get this result:

NOTICE: ALTER TABLE will create implicit trigger(s) for FOREIGN KEY
check(s)
ERROR: rc_ce referential integrity violation - key referenced from
coursesevaluations not found in rcourseinfo

What this is telling you is not that there is any problem with your
formulation of the constraint (which as far as I can tell is what you
want), but that the existing data in the tables violates the constraint
you're trying to impose. If you do something like

SELECT rcoursesevaluations.courseid
FROM rcoursesevalutations NATURAL LEFT JOIN rcourseinfo
WHERE rcourseinfo.courseid IS NULL

you should see which courseids appear in rcoursesevaluations but not in
rcourseinfo.

Richard

On Tue, 8 Jun 2004, Michelle Murrain wrote:

I'm trying to do something which seems really simple to me. (Postgres 7.3.4)

I've got this table:

charter_dev2=# \d rcourseinfo
Table "public.rcourseinfo"
Column | Type | Modifiers
-------------+-----------------------+---------------------------------------------------
courseid | integer | not null default
nextval('rcourseinfo_seq'::text)
coursename | character varying(50) |
dept | character varying(30) |
number | character varying(4) |
section | character varying(2) |
trimester | character varying(5) |
schoolyear | character varying(8) |
facultyid | integer |
description | text |
credits | real |
Indexes: rcourseinfo_pkey primary key btree (courseid),
rcourseinfo_number_index btree (number)

With a primary key called 'courseid'.

I've got a second table:

charter_dev2=# \d coursesevaluations
Table "public.coursesevaluations"
Column | Type | Modifiers
-----------------------+---------+----------------------------------------------------------
courseid | integer |
evalid | integer |
coursesevaluations_id | integer | not null default
nextval('coursesevaluations_seq'::text)
Indexes: coursesevaluations_pkey primary key btree (coursesevaluations_id),
coursesevaluations_evalid_index btree (evalid)

I'd like to make 'courseid' in this second table a foreign key,
referencing 'courseid' in the first table. So I did this command:

charter_dev2=# ALTER TABLE coursesevaluations ADD CONSTRAINT rc_ce
FOREIGN KEY (courseid) REFERENCES rcourseinfo (courseid);

And I get this result:

NOTICE: ALTER TABLE will create implicit trigger(s) for FOREIGN KEY check(s)
ERROR: rc_ce referential integrity violation - key referenced from
coursesevaluations not found in rcourseinfo

This doesn't make any sense to me - the fields are named the same,
and are the same data type. I've pored over the docs, to no avail.
I'm sure I'm missing something really elementary, but it's escaping
me.

That's the message for the constraint violation. It looks like perhaps
the data doesn't meet the constraint (in 7.4 it would have shown you
values, for 7.3 you'll have to look yourself).