[drMerry]

authors:#=<n>

That's what I was looking for for A and B.
I knew calibre had advanced options I could not remember

But Kovid's last reaction is true for C.

I have made some other queries to find some more info.

Does one of you know how to put this in a plugin?

I did make these queries:
# of books per tag (already available in browser)
# of tags per book (the mentioned search will show this)
# tags per author.
Not available yet (as far as I know)

The sql I use is:

SELECT authors.name, COUNT(DISTINCT books_tags_link.tag) AS NumberOfTags
FROM books_tags_link INNER JOIN books_authors_link
ON books_tags_link.book = books_authors_link.book JOIN authors
ON authors.id = books_authors_link.author
GROUP BY authors.name
ORDER BY NumberOfTags

How can I put this in a plugin?