CREATE OR REPLACE FUNCTION public.buy (
  cat_id integer,
  icount integer,
  email varchar
)
RETURNS TABLE (
  error_code integer,
  uid uuid
) AS
$body$
DECLARE
  UID_value uuid:=md5(random()::text || clock_timestamp()::text);
  upcopunt integer;
  my_basket_id integer;
  integer_var integer;
  error_code integer = 0;
BEGIN
SAVEPOINT my_savepoint;

-- создать покупку в корзине и вернуть ее -+id
insert
into shop_basket(email, uid, datetime)
values (email, UID_value, now())
RETURNING id INTO my_basket_id;

-- витащить товар в достаточном количестве
UPDATE
	shop_goods s
SET
	basket_id=my_basket_id
FROM
(
select
      s.id,
      s.basket_id
  from
      shop_goods as s
  where
      	s.cats_id=cat_id
 	and s.basket_id is NULL
  order by s.datetime
  limit icount
) AS s2
where s.id=s2.id;

-- не хватает товара
GET DIAGNOSTICS integer_var = ROW_COUNT;
IF integer_var <> icount THEN
	BEGIN
	error_code=-2;
    ROLLBACK TO my_savepoint;
    END;
END IF;
COMMIT;

RETURN QUERY select error_code, UID_value;

END;
$body$
LANGUAGE 'plpgsql'
VOLATILE
RETURNS NULL ON NULL INPUT
SECURITY INVOKER
COST 100 ROWS 1;