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

Answer 1

you would probably need to use GROUP BY and group it by ID or such:

SELECT 
    folders.*,
    COUNT(files.*) as filetotal 
FROM folders 
    LEFT JOIN files ON folders.ID=files.folderID 
WHERE userId = 16 
GROUP BY folders.ID

Answer 2

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

Answer 3

select 
    f.`folder`,
    f.`userId`,
    r.`count`

from
    `folders` f
    left join 
    (
        select 
            `Folder`,
            count(`id`) `count`

        from `files`

            group by `Folder`
    ) r
        on r.`Folder`=f.`folder`

where 
    `userId`=16

if you do not want to use the group by statement.

i had a simmilar problem in a product list where i wanted to count the star rating of a product in another table [1-5] and the amount of users that voted for that specific product.

Answer 4

Do a sub query that groups by the Folders to get the count per folder, then join it to the first query like this:

    select
       f.*
       fc.Files
    from
       Folders f
--
       -- Join the sub query with the counts by folder     
       JOIN (select
               Folder,
               count(*) Files
             from
                files
             group by
                Folder ) as fc
          on ( fc.Folder = f.Folder )
    where
       f.userid = 16