SQL complex select - sql

Question

I have 2 SQL tables.
for Books:
create table product
(
product_id number primary key
name varchar2(128 byte) not null,
rrp number not null,
available_from date not null
);
and for Orders:
create table orders
(
order_id number primary key,
product_id number not null,
quantity number not null,
order_price number not null,
dispatch_date date not null,
foreign key (product_id) references product(product_id)
);
How to write a query to find books that have sold fewer than 10 copies in the last year, excluding books that have been available for less than 1 month?
I expect this would be smth like:
SELECT name FROM products WHERE
today - products.available_from >= 30
AND
10 > (SELECT COUNT(product_id) FROM orders WHERE orders.product_id = products.product_id AND today - products.dispatch_date <= 365)

Answer 1

On SQL Server this will be something like...............
Select B.ProductId, B.Name, SUM(O.quantity) as OrderedAmount
FROM Books B
INNER JOIN Orders O ON O.product_id = B.ProductId
WHERE
B.available_from <= DateAdd( month, -1, GETDATE()) --Exclude 1 month books
AND O.OrderDate BETWEEN DateAdd( year, -1, GETDATE()) AND GETDATE() --Ordered in the last year
GROUP BY
B.ProductId, B.Name
HAVING SUM(O.quantity) < 10 --Sum of quantity ordered less than 10

Answer 2

On Oracle:
SELECT p.name
FROM product p
LEFT JOIN orders o ON p.product_id=o.product_id -- makes sure books with no orders are also included
WHERE
(p.available_from < add_months(sysdate,-1) -- available for 1 month or more
AND
(o.DISPATCH_DATE IS NULL -- books with no rows in "orders"
OR
p.PRODUCT_ID IN -- books that have sold fewer than 10 copies in last year
(SELECT product_id
FROM ORDERS
WHERE dispatch_date > add_months(sysdate,-12)
GROUP BY product_id
HAVING SUM(quantity) < 10)
)
);