sql - MySQL statement combining a join and a count?

Question

I've got a table of 'folders'. I want to return all the records with the userId of 16.

SELECT * FROM `folders` WHERE userId = 16;

I've got a table of 'files'. For each 'folder' returned above, I want to return a count of 'files' within that 'folder'.

SELECT COUNT(*) as "Files" FROM files WHERE Folder = n;

How do I combine these? I'm lost. Thanks!

Answer 1

SELECT  fol.*
 ,      (       SELECT  COUNT(*)
                FROM    files           fil
                WHERE   fil.Folder      = fol.Folder
        )       AS      "Files"
FROM    folders         fol
WHERE   fol.userId      = 16

It's called a correlated subquery.

http://dev.mysql.com/doc/refman/5.1/en/correlated-subqueries.html