Select to the database, how to deal with COUNT?

Question

SQL

Here's the catch. You need to enter a table that contains a list of books and the number of authors who wrote books in a given genre
. Here is what I did but see an error (
SELECT book.type_book, COUNT(name_author)
FROM author, book WHERE author.author_ID=book.book_ID;

Answer 1

Missing GROUP BY:

SELECT book.type_book, COUNT(author.name_author)
FROM book 
left join author on author.author_ID=book.author_ID
group by book.type_book