Question

I have a table containing a list of folders, each folder has an ID and Description

SELECT * FROM folders

_id |   description
---------------------------
1   |   default
2   |   test

I have an images table that contains a list of images, each image has a folderid

select folderid, count(*) as imagecount from images GROUP BY folderid;

folderid|   imagecount
---------------------------
1       |   4
2       |   5

I want to be able to write a query that returns a list of all folders, with its description, and how many images is inside it

?????

_id |   description |   imagecount
------------------------------------------------------
1   |   default     |   4
2   |   test        |   5

I tried the following query:

SELECT _id, description from folders, (select folderid, count(*) as imagecount from images GROUP BY folder) WHERE _id = folderid;

However it doesn’t work, because it doesn’t return the imagecount column. Any ideas?

Answer 1

This is also a valid SQLite query that will return the answer to your question: how many images in each folder?

        select f.description, sum ( case when i.folderid is null then 0 else 1 end ) as imagecount 
        from folders f left join images i on i.folderid = f.id
        group by f.description

or instead of the sum() with a case statement you could just do count(i.folderid) as imagecount