Robert MannI wrote:
Hello!
I have three tables, mapping out a n:n relationship of authors and the
books they worked on:
table 1: authors (id, name)
table 2: authorships (author_id, book_id)
table 3: books (id, name, bestseller tinyint)
Here's two different queries I want to run:
1. Select each author, and how many books he has worked on.
SELECT a.id, a.name, COUNT(b.id) AS oeuvre FROM authors AS a
LEFT JOIN authorships AS asp ON asp.author_id = a.id
LEFT JOIN books AS b ON asp.book_id = b.id
GROUP BY a.id;
This will also take into account books whose authorship is shared.
2. Select each author, and how many bestseller books (bestseller = 1)
he has worked on.
SELECT a.id, a.name, COUNT(b.id) AS bestsellers FROM authors AS a
LEFT JOIN authorships AS asp ON asp.author_id = a.id
LEFT JOIN books AS b ON asp.book_id = b.id
WHERE b.bestseller = 1
GROUP BY a.id;
Only added the WHERE clause and changed the 3rd column name.
HTH
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