Please could you help me with a query?

Question

Please could someone help with the following query? I have 3 tables:
Books
BookCode........Name
1.....................          Book1
2.....................          Book2
3.....................          Book3
4     .....................     Book4
5          .....................Book5
Categories
Catname.....................          BookCode
Sport          .....................1
Sport          .....................2     
Sport          .....................3
News          .....................2
News          .....................3
News          .....................4
NonFict          .....................2
NonFict          .....................5
Modern          .....................1
Modern          .....................2
Modern          .....................5
Old          .....................3
Old          .....................4
Stock
CatName     .....................Stocked
Sport          .....................1          
News          .....................1
NonFict          .....................NULL
Modern          .....................NULL
Old          .....................1
I need a query that selects all books.name where ALL of the book's related category names have stock records of NULL. So if the book is in 3 categories, all those categories need to be NULL in the stock table for a value to be returned.
Thanks very much.

Answer 1

And here's another way using a set operator:
SQL> select b.name
  2        ,count(*) cat_total
  3  from   books b
  4        ,categories c
  5        ,stock s
  6  where  b.bookcode = c.bookcode
  7  and    c.catname  = s.catname
  8  group  by b.name
  9  intersect
10  select b.name
11        ,count(*) cat_total
12  from   books b
13        ,categories c
14        ,stock s
15  where  b.bookcode = c.bookcode
16  and    c.catname  = s.catname
17  and    s.stocked is null
18  group  by b.name
19  ;
NAME             CAT_TOTAL
Book5                    2