In postgres I am fairly sure you can do something like this
SELECT
authors.stage_name,
count(select id from books where books.author_id = authors.id)
FROM
authors,
books;
Essentially, in this example I would like to return a list of authors and how many books each has written.... in the same query.
Is this possible? I suspect this approach is rather naive..
Thanks :)
Well, for one thing, it returns a Cartesian product of all authors to all books, regardless of whether that author wrote that book.
Here's how I'd write a query to get the result you say you want:
SELECT a.stage_name, COUNT(b.id)
FROM authors a
LEFT OUTER JOIN books b ON (a.id = b.author_id)
GROUP BY a.id;
You need to learn how to write join queries if you use SQL. The join is to SQL what the loop is to application programming languages. I.e. it's a fundamental programming construct that you need to know.
How about using a join:
SELECT authors.stage_name, count(*)
FROM authors INNER JOIN books on books.author_id = authors.id
GROUP BY authors.stage_name
