Thread: Using new.id in the WHERE condition of one UPDATE inside ON INSERT rule
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 ASON INSERT TO my_tableDO 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 = (SELECTMAX(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 --
Aron <auryn@wanadoo.es> 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
On Jueves 25 Febrero 2010 16:28:56 usted escribió: > Aron <auryn@wanadoo.es> 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 ' DECLAREchange_other BOOL; BEGINIF (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();