Re: 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
> --
> IT consulting, training, international recruiting
> http://www.allaroundtheworld.fr/.
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--
Adrian Klaver
adrian(dot)klaver(at)gmail(dot)com