SQL, update column in a specific row, instead of all rows - sql

Question

The task is to update the specific row in the column klienta_nr, which is located in the table klientu_ieteikumi. If a specific row is deleted in klienti table. This code updates the whole column not the specific row. What is the problem?
CREATE FUNCTION "funkc"() RETURNS "opaque" AS '
DECLARE
BEGIN
IF (TG_OP = ''DELETE'') THEN
UPDATE klientu_ieteikumi SET klienta_nr = NULL ;
END IF;
RETURN NEW;
END;
' LANGUAGE 'plpgsql';
CREATE TRIGGER "triger"
AFTER DELETE ON "klienti"
FOR EACH ROW EXECUTE PROCEDURE funkc();
This one did what I wanted, thanks anyway everyone :)
CREATE FUNCTION "funkcija1"() RETURNS TRIGGER AS $$
BEGIN
UPDATE klientu_ieteikumi SET klienta_nr = NULL
FROM klienti WHERE old.klienta_nr = klientu_ieteikumi.klienta_nr;
RETURN NEW;
END;
$$ LANGUAGE plpgsql;
CREATE TRIGGER "trigeris"
AFTER DELETE ON "klienti"
FOR EACH ROW EXECUTE PROCEDURE funkcija1();

Answer 1

you need a WHERE clause to restrict the number of rows affected by the statement.
edit:
UPDATE klientu_ieteikumi
SET klienta_nr = NULL
WHERE klienta_ieteikumi.klienta_nr = klienti.klienta_nr

Answer 2

You presented "solution" cannot work and is wrong in a sneaky way.
CREATE FUNCTION funkcija1()
RETURNS TRIGGER AS
$func$
BEGIN
CREATE FUNCTION funkcija1()
RETURNS TRIGGER AS
$func$
BEGIN
UPDATE klientu_ieteikumi
SET klienta_nr = NULL
FROM klienti -- !!
WHERE klientu_ieteikumi.klienta_nr = OLD.klienta_nr;
RETURN NEW;
RETURN NULL;
END
$func$ LANGUAGE plpgsql;
CREATE TRIGGER trigeris
AFTER DELETE ON klienti
FOR EACH ROW EXECUTE PROCEDURE funkcija1();
There is no NEW in an AFTER trigger. This wouldn't work at all and raise an exception immediately.
The unbound (and utterly pointless) table klienti in the FROM clause leads to a CROSS JOIN. I.e., instead of just one time, the UPDATE is executed as many times as there are rows in klienti. This would be a major drag on performance, and you might never find out, since there is no error message. Just a lot of wasted cycles and table bloat on your server.