The following seems to work, but I don't feel confident this is really
the correct code:
CREATE RULE shoe_upd AS
ON UPDATE TO shoe
DO INSTEAD (
UPDATE shoes
SET sh_name = NEW.sh_name, sh_avail = NEW.sh_avail
WHERE shoes.sh_id = NEW.sh_id;
INSERT INTO shoelaces (sh_id, sl_name)
SELECT New.sh_id, New.sl_name WHERE New.sl_name IS NOT NULL;);
I could find out doing a number of tests, but it would be good to
understand what is going on.
--
Seb