Question

I have two tables

documents: id, folder_id

folders: id, title

I want to retrieve a list of folders and count of how many files relate to that folder (documents.folder_id = folders.id)

I tried this

select 
 f.title, count(d.id) as file_count
from
 folders f
left join
 documents d on f.id = d.folder_id

But that only returns one row, with the total number of rows in the documents table

Answer 1

You’re missing a GROUP BY clause to return a row per f.title.

select 
 f.title, count(d.id) as file_count
from
 folders f
left join
 documents d on f.id = d.folder_id
GROUP BY f.title

Note that the above will omit empty folders, I believe. If you want a zero count for the empty folders, use COUNT(d.*) instead:

select 
 f.title, count(d.*) as file_count
from
 folders f
left join
 documents d on f.id = d.folder_id
GROUP BY f.title