Question on "tying" two queries together

Question

I get an error when I run the following code (shown below).
Why can't I "tie" these 2 queries together like this?
Both run fine by themselves and give me good data, I just need to tie them together.
This is for a beginning sql class, so I all I really want is an explanation as to why this is not allowed.
I'm not finding the answer in the book I have.
Any insight for a newb appreciated!
SQL> SELECT order#, isbn, title, SUM(quantity) AS SubTotal
2        FROM orderitems RIGHT OUTER JOIN books USING (isbn)
3        GROUP BY order#, isbn, title
4        ORDER BY order#
5 WHERE (isbn, title) IN
6                     (SELECT isbn, title
7                       FROM books
8                       WHERE retail - cost >
9                                        (SELECT AVG(SUM(retail - cost))
10                                         FROM books
11                                        GROUP BY isbn));
WHERE (isbn, title) IN
ERROR at line 5:
ORA-00933: SQL command not properly ended

Answer 1

Hi,
When the following clauses are used, they always have to be in this order:
WHERE
GROUP BY
ORDER BY
You can skip any (or all) of these, but when you use them, they have to come in that order.
Move the WHERE-clause (the whole thing, up to, but not including, the semicolon) before the GROUP BY clause.