CREATE FUNCTION skip_update() RETURNS trigger AS $$
	BEGIN
		RETURN NULL;
	END;
$$ LANGUAGE plpgsql;
CREATE FUNCTION fail_update() RETURNS trigger AS $$
	BEGIN
		RAISE EXCEPTION 'can''t modify row values for existing primary key';
	END;
$$ LANGUAGE plpgsql;
CREATE TABLE Dummy_Test (
	Timestamp TIMESTAMP WITH TIME ZONE PRIMARY KEY,
	Foo TEXT,
	Bar TEXT
);
CREATE TRIGGER Dummy_Test_dupe BEFORE UPDATE ON Dummy_Test FOR EACH ROW
	WHEN ( OLD.Timestamp IS NOT DISTINCT FROM NEW.Timestamp AND OLD.Foo IS NOT DISTINCT FROM NEW.Foo AND OLD.Bar IS NOT DISTINCT FROM NEW.Bar )
	EXECUTE FUNCTION skip_update();
CREATE TRIGGER Dummy_Test_modify BEFORE UPDATE ON Dummy_Test FOR EACH ROW
	WHEN ( OLD.Foo IS DISTINCT FROM NEW.Foo OR OLD.Bar IS DISTINCT FROM NEW.Bar )
	EXECUTE FUNCTION fail_update();

INSERT INTO Dummy_Test (Timestamp,Foo,Bar) VALUES ('2020-01-02 12:34','Hello','World') ON CONFLICT ON CONSTRAINT Dummy_Test_pkey DO UPDATE SET Foo=EXCLUDED.Foo, Bar=EXCLUDED.Bar;
INSERT INTO Dummy_Test (Timestamp,Foo,Bar) VALUES ('2020-01-02 12:34','Hello','World') ON CONFLICT ON CONSTRAINT Dummy_Test_pkey DO UPDATE SET Foo=EXCLUDED.Foo, Bar=EXCLUDED.Bar;
INSERT INTO Dummy_Test (Timestamp,Foo,Bar) VALUES ('2020-01-02 12:34','Hello','abcde') ON CONFLICT ON CONSTRAINT Dummy_Test_pkey DO UPDATE SET Foo=EXCLUDED.Foo, Bar=EXCLUDED.Bar;