Altering parent table breaks child table defaults

On 10/07/2013 07:51 AM, Ovid wrote:

Hi all,

This problem has also been posted to Stack
Overflow. http://stackoverflow.com/questions/19227920/altering-a-parent-table-in-postgresql-8-4-breaks-child-table-defaults

The problem: In Postgresql 8.4 (not tested on other versions), if table
`temp_person_two` inherits from`temp_person`, default column values on
the child table are ignored if the *parent* table is altered.

How to replicate (these don't need to be temporary tables. I made them
temporary for your cut-n-paste convenience):

First, create table and a child table. The child table should have one
column that has a default value.

CREATE TEMPORARY TABLE temp_person (
person_id SERIAL,
name VARCHAR
);

CREATE TEMPORARY TABLE temp_person_two (
has_default character varying(4) DEFAULT 'en'::character
varying NOT NULL
) INHERITS (temp_person);

Next, create a trigger on the parent table that copies its data to the
child table (I know this appears like bad design, but this is a minimal
test case to show the problem).

CREATE FUNCTION temp_person_insert() RETURNS trigger
LANGUAGE plpgsql
AS '
BEGIN
INSERT INTO temp_person_two VALUES ( NEW.* );
RETURN NULL;
END;
';

CREATE TRIGGER temp_person_insert_trigger
BEFORE INSERT ON temp_person
FOR EACH ROW
EXECUTE PROCEDURE temp_person_insert();

Then insert data into parent and select data from child. The data should
be correct.

INSERT INTO temp_person (name) VALUES ('ovid');
SELECT * FROM temp_person_two;
person_id | name | has_default
-----------+------+-------------
1 | ovid | en
(1 row )

Finally, alter the parent table by adding a new, unrelated column.
Attempt to insert data and watch a "not-null constraint" violation occur:

ALTER TABLE temp_person ADD column foo text;
INSERT INTO temp_person(name) VALUES ('Corinna');
ERROR: null value in column "has_default" violates not-null constraint
CONTEXT: SQL statement "INSERT INTO temp_person_two VALUES ( $1 .* )"
PL/pgSQL function "temp_person_insert" line 2 at SQL statement

What happens if you do?:

INSERT INTO temp_person(name, has_default) VALUES ('Corinna', DEFAULT)

My guess is the problem is the expansion of NEW.* is leading to
VALUES('Corina', NULL)

My version:

testing=# select version();
version

-------------------------------------------------------------------------------------------------------
PostgreSQL 8.4.17 on x86_64-pc-linux-gnu, compiled by GCC
gcc-4.4.real (Debian 4.4.5-8) 4.4.5, 64-bit
(1 row)

Cheers,
Ovid
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