Question

I’d like to create an SQL statement that will tell me how many books where written by a given author.

When you know the authorid (foreign key to books table) it’s easy:

select count(*) from books where authorid = 25;
15

You can see that author with id 15 has written 15 books. Is it possible to create a statement for all the authors such that the ouput is as follows?

author_id, author_name, number_of_books
1          Michael      15
2          Robin        7
...

Answer 1

You could do this with a group by clause:

select 
    a.author_id,
    a.author_name,
    count(*) as number_of_books
from
    authors a inner join
    books b on b.author_id = a.author_id
group by
    a.author_id,
    a.author_name
order by 
    number_of_books