CREATE TABLE "public"."persons" ( 
	"id" Integer DEFAULT nextval('person_id_seq'::regclass) NOT NULL,
	"surname" Character Varying( 100 ) NOT NULL,
	"name" Character Varying( 100 ) NOT NULL,
	"patronymic" Character Varying( 100 ),
	"date_birth" Date NOT NULL,
	"place_birth" Character Varying( 1000 ) NOT NULL,
	"parent_id" Integer,
	"surnamepat" Character Varying,
	"surnamepat_short" Character Varying,
	PRIMARY KEY ( "id" ) );

CREATE TABLE "public"."history_legal_representatives" ( 
	"id" Integer DEFAULT nextval('history_legal_representative_id_seq'::regclass) NOT NULL,
	"person_id" Integer NOT NULL,
	"person_parent_id" Integer NOT NULL,
	"modified" Date DEFAULT ('now'::text)::date,
	PRIMARY KEY ( "id" ) );

"person_id" - Человек (в таблице persons - id)
"person_parent_id" - Законный представитель (в таблице persons - parent_id)

CREATE TRIGGER addrep BEFORE INSERT ON "public"."persons" FOR EACH ROW EXECUTE PROCEDURE addrepresentative()

CREATE OR REPLACE FUNCTION public.addrepresentative()
 RETURNS trigger
 LANGUAGE plpgsql
AS $function$
BEGIN
	if NEW.parent_id != NULL then
	insert into history_legal_representatives (person_id, person_parent_id) 
	values (NEW.id, NEW.parent_id);
	end if;
	RETURN NEW;
END;
$function$

CREATE TRIGGER delrep BEFORE UPDATE ON "public"."persons" FOR EACH ROW EXECUTE PROCEDURE delrepresentative()

CREATE OR REPLACE FUNCTION public.delrepresentative()
 RETURNS trigger
 LANGUAGE plpgsql
AS $function$
BEGIN
	if NEW.parend_id = null then
	delete from history_legal_representatives where id = NEW.id;
	end if;
	RETURN NEW;
END;
$function$