Oracle SQL Update a column based on another table but based on a date - sql

Question

Learning SQL so please forgive me.
I have a table that holds many accounts(and sub accounts) and another table that holds many orders they are custom tables taken from different databases.
What I am trying to do is update order_amt on the account table with the order_val value from the orders table but if there are more than one order with that account I want the order amount from the earliest order date only.
Account Table
Acc _Num..........Comp_Name.......Order_Amt.......Int_Id
123456789-1.....ABC Ltd.......................................123456789
123456789-2.....ABC Ltd.......................................123456789
987654321-1.....Xyz Ltd.........................................987654321
987654321-2.....Xyz Ltd.........................................987654321
Orders Table
Order_Num.....Order_Dt.....Order_Val.....Acc_num
1......................01/01/13......£20.00...........123456789
2......................01/01/14......£10.00...........123456789
3......................01/01/10......£100.00..........987654321
4......................01/01/11......£200.00..........987654321
So the order_amt for accounts 123456789-1 & 2 = £20.00 and from 987654321-1 & 2 would be £100.00.
UPDATE accounts a
SET a.order_amt =
(
SELECT order_val
FROM orders o
WHERE a.int_id = o.acc_num
AND EXISTS
(
SELECT MIN(order_dt)
FROM orders oa
WHERE o.order_num = oa.order_num
);
I am getting a few errors including the error that more than one row returned? Could anyone please help me?
kind Regards
Eden

Answer 1

I think you need something like this:
UPDATE accounts a
SET a.order_amt =
(
SELECT order_val
FROM orders o
WHERE a.int_id = o.acc_num
GROUP BY order_val
HAVING order_dt = MIN(order_dt);
);

Answer 2

Create a FK on the column account_number inside of the orders table and have it reference the auto-increment account id of the accounts table.
Then as Roger suggest, with the slight modification of the column int_id AND a modification of the HAVING clause
UPDATE accounts a
SET a.order_amount =
(
SELECT order_value
FROM orders o
WHERE a.account_number = o.account_number
GROUP BY order_value
HAVING MIN(order_date)
)
This will not fix the error that is occurring with more than one row being returned though since there are multiple orders with the same account id attached to them. You will need to be more specific about how what you are needing. Do you want the average of all order amounts to equal the order value in the accounts table? Or maybe the MAX/MIN value?