Consider the following relation schema :
Book (ISBN, title, category, pid)
Publisher (Pid, Pname, address)
What does the below query return?
\(\left( {{\pi _{Pname,category}}\left( {Publisher⋈Book} \right)} \right) \div \left( {{\pi _{category}}\left( {Book} \right)} \right)\)
1
Find the name of the publishers who have published all categories of books
2
Find the name of the publishers who have published a specific category of books
3
Find the name of the books published by all the publishers
4
None of the above