CREATE TABLE b
(
	b_id serial,
	a_id integer,
	bdata text,
	PRIMARY KEY (b_id)
	--DEFERRABLE INITIALLY DEFERRED
)
;

CREATE TABLE a
(
	a_id serial,	
	adata text,
	PRIMARY KEY (a_id)
	--DEFERRABLE INITIALLY DEFERRED
)
;
--=================================
-- Function: ftr_bu_b()
-- без изысков и забот о безусловной целостности:
CREATE OR REPLACE FUNCTION ftr_biud_b()
  RETURNS trigger AS
$BODY$
--BEFORE UPDATE,DELETE
DECLARE
BEGIN
	
	IF TG_OP = 'DELETE' THEN
		UPDATE a SET adata=a_id||'.'||(SELECT string_agg(b_id::text,'.') FROM b WHERE b.a_id=OLD.a_id)
		WHERE a.a_id=OLD.a_id;
		
		RETURN OLD;	
	ELSE
		UPDATE a SET adata=a_id||'.'||(SELECT string_agg(b_id::text,'.') FROM b WHERE b.a_id=NEW.a_id)
		WHERE a.a_id=NEW.a_id;
		IF TG_OP = 'UPDATE' THEN
			IF OLD.a_id<>NEW.a_id THEN
				UPDATE a SET adata=a_id||'.'||(SELECT string_agg(b_id::text,'.') FROM b WHERE b.a_id=OLD.a_id)
				WHERE a.a_id=OLD.a_id;
				RETURN OLD;	
			END IF;
		END IF;

		RETURN NEW;
	END IF;	

END;
$BODY$
  LANGUAGE plpgsql VOLATILE SECURITY DEFINER
  COST 100;


CREATE TRIGGER tr_biud_b BEFORE INSERT OR UPDATE OR DELETE
   ON b FOR EACH ROW
   EXECUTE PROCEDURE public.ftr_biud_b();
--======================================

INSERT INTO a (a_id) values (1),(2),(3),(4);
--test:
SELECT * FROM a;
-------------
INSERT INTO b (a_id,b_id) VALUES 
	(1,-1),(1,-2),(1,-3)
	,(2,-5),(2,-6),(2,-7)
	,(3,-8),(3,-9),(3,-10);
SELECT * FROM a;
DELETE FROM a WHERE a_id=1;
--test:
SELECT * FROM a;
---------------
/*
4;""
2;"2.-5.-6"
3;"3.-8.-9"
*/
-- кудынть делось  a_id = 1 ???? ЧЯДНТ

UPDATE a
SET a_id=-1
WHERE a_id=2;

SELECT * FROM b WHERE a_id IN (-1,2);
SELECT * FROM a WHERE a_id IN (-1,2);

UPDATE b SET a_id=-1  WHERE a_id=2;
SELECT * FROM b WHERE a_id IN (-1,2);
----------------------
select version();--"PostgreSQL 9.3.3 on x86_64-unknown-linux-gnu, compiled by gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-4), 64-bit"

SELECT  t.tgname 
	,pg_get_triggerdef(t.oid) AS src
		FROM pg_class c, pg_trigger t 
		WHERE c.oid = t.tgrelid		
		AND relname = 'a';
-----------------------------------
"RI_ConstraintTrigger_a_109314";"CREATE CONSTRAINT TRIGGER "RI_ConstraintTrigger_a_109314" AFTER DELETE ON a FROM b NOT DEFERRABLE INITIALLY IMMEDIATE FOR EACH ROW EXECUTE PROCEDURE "RI_FKey_cascade_del"()"
"RI_ConstraintTrigger_a_109315";"CREATE CONSTRAINT TRIGGER "RI_ConstraintTrigger_a_109315" AFTER UPDATE ON a FROM b NOT DEFERRABLE INITIALLY IMMEDIATE FOR EACH ROW EXECUTE PROCEDURE "RI_FKey_cascade_upd"()"