Calling a function for each updated row in postgresql - postgresql

Question

I have a sql UPDATE statement in a plpgsql function. I now want to call the pg_notify function for each updated row and am uncertain if my solution is the best possibility.
I am not aware of any position in the UPDATE statement itself where I could apply the function. I don't think it is possible in the SET part and if I would apply the function in the WHERE part, it would be applied to each row as it is checked and not only the updated rows, correct?
I therefore thought I could use the RETURNING part for my purposes and designed the function like this:
CREATE OR REPLACE FUNCTION function_name() RETURNS VOID AS $BODY$
BEGIN
UPDATE table1
SET a = TRUE
FROM table2
WHERE table1.b = table2.c
AND <more conditions>
RETURNING pg_notify('notification_name', table1.pk);
END;
$BODY$ LANGUAGE 'plpgsql' VOLATILE;
Unfortunately this gave me an error saying that I am not using or storing the return value of the query anywhere. I therefore tried putting PERFORM in front of the query but this seemed to be syntactically incorrect.
After trying different combinations with PERFORM my ultimate solution is this:
CREATE OR REPLACE FUNCTION function_name() RETURNS VOID AS $BODY$
DECLARE
dev_null INTEGER;
BEGIN
WITH updated AS (
UPDATE table1
SET a = TRUE
FROM table2
WHERE table1.b = table2.c
AND <more conditions>
RETURNING pg_notify('notification_name', table1.pk)
)
SELECT 1 INTO dev_null;
END;
$BODY$ LANGUAGE 'plpgsql' VOLATILE;
This works as it is supposed to, but I feel like there should be a better solution which does not temporarily store a useless result and does not use a useless variable.
Thank you for your help.
** EDIT 1 **
As can be seen in #pnorton 's answer, a trigger would do the trick in most cases. For me, however, it is not applicable as the receiver of the notifications also sometimes updates the table and I do not want to generate notifications in such a case

Answer 1

"I have a sql UPDATE statement in a plpgsql function. I now want to
call the pg_notify function for each updated row "
Ok I might be tempted to use a trigger Eg
CREATE TABLE foobar (id serial primary key, name varchar);
CREATE OR REPLACE FUNCTION notify_trigger() RETURNS trigger AS $$
DECLARE
BEGIN
PERFORM pg_notify('watch_tb_update', TG_TABLE_NAME || ',id,' || NEW.id );
RETURN new;
END;
$$ LANGUAGE plpgsql;
CREATE TRIGGER foobar_trigger AFTER INSERT ON foobar
FOR EACH ROW EXECUTE PROCEDURE notify_trigger();
LISTEN watch_tb_update;
INSERT into foobar(id, name) values(1,'test_name');
I've tested this and it works fine