MYSQL query using JOIN table - mysql

Question

I have two tables one CUSTOMERS
+-----------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-----------+--------------+------+-----+---------+-------+
| ID | int(11) | NO | PRI | NULL | |
| FIRSTNAME | varchar(50) | YES | | NULL | |
| LASTNAME | varchar(50) | YES | | NULL | |
| ADDRESS | varchar(100) | YES | | NULL | |
+-----------+--------------+------+-----+---------+-------+
and orders
+---------------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------------+--------------+------+-----+---------+-------+
| ID | int(11) | NO | PRI | NULL | |
| PRODUCT_NAME | varchar(100) | YES | | NULL | |
| PRODUCT_PRICE | double(10,4) | YES | | NULL | |
| DATE_ORDER | date | YES | | NULL | |
| ID_CUSTOMER | int(11) | YES | | NULL | |
| AMOUNT | int(11) | YES | | NULL | |
+---------------+--------------+------+-----+---------+-------+
I need to "Get the first and last names of the customers who made orders in total sum greater than the average sum of all orders. Don’t care about duplicates".
Here what I've tried
select FIRSTNAME, LASTNAME, ID,
AVG(PRODUCT_PRICE * AMOUNT)
from CUSTOMERS C
join ORDERS O
on C.ID = ID_CUSTOMER
GROUP BY FIRSTNAME, LASTNAME
HAVING AVG(PRODUCT_PRICE * AMOUNT) < (
select (PRODUCT_PRICE * AMOUNT)
from ORDERS
where C.ID = O.ID_CUSTOMER;
That does not work. I need some help

Answer 1

You need to find average sum of all orders in a subquery.
select
C.ID,
C.FIRSTNAME,
C.LASTNAME,
SUM(O.PRODUCT_PRICE * O.AMOUNT)
from CUSTOMERS C
join ORDERS O
on C.ID = O.ID_CUSTOMER
GROUP BY C.ID, C.FIRSTNAME, C.LASTNAME
HAVING SUM(PRODUCT_PRICE * AMOUNT) > (
select AVG(PRODUCT_PRICE * AMOUNT)
from ORDERS)

Answer 2

Most part of your code is correct, you want just remove the part where C.ID = O.ID_CUSTOMER;. this is not need to calculate the average value of the order items.
using this following code you can get the required outut
SELECT FIRSTNAME,LASTNAME FROM CUSTOMERS
INNER JOIN ORDERS ON CUSTOMERS.ID=ORDERS.ID_CUSTOMER
GROUP BY CUSTOMERS.ID
HAVING SUM(ORDERS.PRODUCT_PRICE*ORDERS.AMOUNT)>
(SELECT AVG(PRODUCT_PRICE*AMOUNT) FROM ORDERS)