これはおそらく単純な構文エラーですが、1 時間調べてみましたが、見つかりません。別の見方をすれば、正しい方向に進むことができるのではないでしょうか??
select
lname +', '+ Fname as "Author Name"
from
Author a
join
BOOKAUTHOR ba on a.AuthorID = ba.authorid
where
ba.isbn = (select ba.isbn
from
(select
ROW_NUMBER() over (order by sum(quantity) desc) as "Placement",
b.isbn,
sum(QUANTITY) as "Total"
from
ORDERITEMS oi
join
Books b on b.ISBN = oi.isbn
group by
b.ISBN)
where Placement = 1) --the "WHERE" is giving me an error.