SQL Server 2012，嵌套的select语句，语法错误？？我看不出来

这可能是一个简单的语法错误，但我已经看了一个小时，我就是找不到它，也许另一双眼睛可以帮我指出正确的方向

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. 

---

当FROM子句将派生表指定为表源时，必须为子查询指定别名：

select lname +', '+ Fname as "Author Name"
from Author a
join BOOKAUTHOR ba on
a.AuthorID = ba.authorid
where ba.isbn = 
       (select q.isbn -- <== notice the "q"
        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) q -- <== notice the "q"
        where Placement = 1)

从：

---

当FROM子句将派生表指定为表源时，必须为子查询指定别名：

select lname +', '+ Fname as "Author Name"
from Author a
join BOOKAUTHOR ba on
a.AuthorID = ba.authorid
where ba.isbn = 
       (select q.isbn -- <== notice the "q"
        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) q -- <== notice the "q"
        where Placement = 1)

从：

---

AKA，为派生表别名，如Michael所说。查询的外部部分希望在外部查询中将其命名为baI，将ba.isbn更改为q.isbn以避免混淆。AKA，为派生表别名，正如Michael所说，查询的外部部分希望将其命名为baI，并在外部查询中将ba.isbn更改为q.isbn，以避免混淆。