Aggregation using subquery: Error 1111 occurs. How do I fix it? - mysql

Question

Please understand that I used Google Translator because I am not proficient in English.
First of all, I get error 1111 when using mysql.
The problem is to find the name of the customer whose average book table sales is higher than the average of each customer in the customer table.
Currently, the code I have written is:
1)
select customer.name from customer, Orders
where avg(Orders.saleprice) <
(select avg(Orders.saleprice) from Orders, customer
where Orders.custid = customer.custid AND Orders.custid = 1
group by orders.custid);
select customer.name from customer, Orders, book
where avg(Orders.saleprice) <
(select avg(Orders.saleprice) from Orders, customer
where Orders.custid = customer.custid group by orders.custid);
In the case of 2), I tried to compare values at a time, but the code failed because error 1111 occurred. In the case of 1), the code was written with only one custid set to '1'.
The picture above is the average of the purchase amount of each customer in each customer table.
The picture above is the average of the sales of the book table.
This is my first time using stackoverflow recommended by a subscribed YouTuber, so I am inexperienced and English is also inexperienced, but any help would be greatly appreciated.

Answer 1

You can solve the problem by next way:
-- select customers with average salesprice
select
customers.*,
avg(saleprice) as avgsaleprice
from customers
join orders on customers.id = orders.customer_id
group by customers.id, customers.name
-- filter result for customers having average greater then common order average
having avgsaleprice > (
select
avg(saleprice) as avgsaleprice
from orders
);
Look the fiddle at SQLize.online