[SQL] Using new.id in the WHERE condition of one UPDATE inside ON INSERT rule

[Aron]

I would like to avoid using "SELECT MAX(id) FROM my_table" (it doesn't seem a 
good method), but if I use "new.id", I get new id values, not the "id" 
inserted with the rule, and the condition is always false.

Complete example (it works because it doesn't use new.id inside condition):

DROP TABLE IF EXISTS my_table;
DROP TABLE IF EXISTS my_other_table;

CREATE TABLE my_other_table (
id serial PRIMARY KEY,
my_other_cost INTEGER
);

INSERT INTO my_other_table(my_other_cost) VALUES(155);
INSERT INTO my_other_table(my_other_cost) VALUES(277);

CREATE TABLE my_table (
id serial PRIMARY KEY,
id_other INTEGER,
my_cost INTEGER
);

CREATE OR REPLACE RULE my_insert AS
ON INSERT TO my_table
DO ALSO
UPDATE my_table SET my_cost = my_other_table.my_other_cost
FROM my_other_table
WHERE new.id_other = my_other_table.id
AND my_table.id = (SELECT MAX(id) FROM my_table); -- I want " = 
new.id" 
here, but doesn't work as I expect

INSERT INTO my_table(id_other) VALUES(1);
INSERT INTO my_table(id_other) VALUES(2);

SELECT * FROM my_table;


Thanks
-- 


-- 
Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-sql

Re: [SQL] Using new.id in the WHERE condition of one UPDATE inside ON INSERT rule

[Aron]

On Jueves 25 Febrero 2010 16:28:56 usted escribió:
> Aron  writes:
> > I would like to avoid using "SELECT MAX(id) FROM my_table" (it doesn't
> > seem a good method), but if I use "new.id", I get new id values, not the
> > "id" inserted with the rule, and the condition is always false.
> 
> "new.id" is a macro, which in this example will be expanded into a
> nextval() function call, which is why it doesn't work --- the nextval()
> in the WHERE condition will produce a different value from the one in
> the original INSERT.  You would be far better off using a trigger here
> instead of a rule.
> 
>   regards, tom lane
> 
Thank you very much.
I've used this trigger succesfully:

CREATE OR REPLACE FUNCTION copy_cost RETURNS "trigger" AS '
DECLARE
change_other BOOL;
BEGIN
IF (tg_op = ''UPDATE'') THEN
IF (new.id_other <> old.id_other) THEN
change_other = true;
ELSE
change_other = false;
END IF;
END IF;

IF (tg_op = ''INSERT'' AND new.my_cost IS NULL)
OR change_other) THEN
new.my_cost = (
SELECT my_other_cost
FROM my_other_table
WHERE id = new.id_other
);
END IF;
RETURN NEW;
END;
' LANGUAGE 'plpgsql';

CREATE TRIGGER copy_cost__trigger
BEFORE INSERT OR UPDATE ON my_table
FOR EACH ROW
EXECUTE PROCEDURE copy_cost();

-- 
Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-sql