PostgreSQL: UPDATE using aggregate function

Question

I want to update the table paneldata setting the column ibase using an aggregate function.

UPDATE paneldata p
SET ibase=SUM(1/i.dist)
FROM ibaselang i
WHERE p.gid=i.gid
AND i.instp<p.period

This results in ERROR: aggregate functions are not allowed in UPDATE

TABLE DEFINITIONS

CREATE TABLE public.ibaselang
(
  gid integer,
  dist double precision,
  buildid integer,
  instp smallint
)
WITH (
  OIDS=FALSE
);

Solution Approach

Unfortunately I don't know how to implement my WHERE functions in a subquery.

Answer 1

Here's a generic example of how to do it.

UPDATE public.customer_value cv
SET total_value = sub_q.sum_val 
FROM 
    (
    SELECT SUM(order_amount) AS sum_val, o.customer_id 
    FROM public.orders AS o
    GROUP BY o.customer_id
    ) AS sub_q
WHERE sub_q.customer_id = cv.customer_id;

If you want to try this example out in full you can create the dummy data like this:

CREATE TABLE public.customer_value
(
  customer_id int 
, total_value numeric (10,2)
);

CREATE TABLE public.orders 
(
  customer_id int
, order_amount numeric(10,2)
);

INSERT INTO public.customer_value
(customer_id)
VALUES 
  (1)
, (2);


INSERT INTO public.orders
(customer_id, order_amount)
VALUES 
 (1, 10)
,(1, 10)
,(2, 7.5)
,(2, 7.5);