Need cleaner update method in PostgreSQL 9.1.3 - postgresql

Question

Using PostgreSQL 9.1.3 I have a points table like so (What's the right way to show tables here??)
| Column | Type | Table Modifiers | Storage
|--------|-------------------|-----------------------------------------------------|----------|
| id | integer | not null default nextval('points_id_seq'::regclass) | plain |
| name | character varying | not null | extended |
| abbrev | character varying | not null | extended |
| amount | real | not null | plain |
In another table, orders I have a bunch of columns where the name of the column exists in the points table via the abbrev column, as well as a total_points column
| Column | Type | Table Modifiers |
|--------------|--------|--------------------|
| ud | real | not null default 0 |
| sw | real | not null default 0 |
| prrv | real | not null default 0 |
| total_points | real | default 0 |
So in orders I have the sw column, and in points I'll now have an amount that realtes to the column where abbrev = sw
I have about 15 columns like that in the points table, and now I want to set a trigger so that when I create/update an entry in the points table, I calculate a total score. Basically with just those three shown I could do it long-hand like this:
UPDATE points
SET total_points =
ud * (SELECT amount FROM points WHERE abbrev = 'ud') +
sw * (SELECT amount FROM points WHERE abbrev = 'sw') +
prrv * (SELECT amount FROM points WHERE abbrev = 'prrv')
WHERE ....
But that's just plain ugly and repetative, and like I said there are really 15 of them (right now...). I'm hoping there's a more sophisticated way to handle this.
In general each of those silly names on the orders table represents a type of work associated with the order, and each of those types has a 'cost' to it, which is stores in the points table. I'm not married to this structure if there's a cleaner setup.

Answer 1

"Serialize" the costs for orders:
CREATE TABLE order_cost (
order_cost_id serial PRIMARY KEY
, order_id int NOT NULL REFERENCES order
, cost_type_id int NOT NULL REFERENCES points
, cost int NOT NULL DEFAULT 0 -- in Cent
);
For a single row:
UPDATE orders o
SET total_points = COALESCE((
SELECT sum(oc.cost * p.amount) AS order_cost
FROM order_cost oc
JOIN points p ON oc.cost_type_id = p.id
WHERE oc.order_id = o.order_id
), 0);
WHERE o.order_id = $<order_id> -- your order_id here ...
Never use the lossy type real for currency data. Use exact types like money, numeric or just integer - where integer is supposed to store the amount in Cent.
More advice in this closely related example:
How to implement a many-to-many relationship in PostgreSQL?