SQL Query to select the COUNT from another SQL query - sql

Question

I'm having a little trouble making an SQL SERVER 2000 query. Here is my scenario:
I have a table called Folders with 3 columns: pk_folderID, folderName and fk_userID.
Also, I have another table called FolderMedia which stores what media (whatever) belong to a certain folder. There are 2 columns: fk_folderID, fk_media.
And the last, I have a table called Media which stores some media details. It has a primary key pk_media and among other columns, it has a MediaType column which tells the type of that media: image or video.
Now, I would like a query that does the following:
Select all folders that belong to a certain fk_userID, and then also get the number of media in that folder. I've seen a query like this here on StackOverflow, but I didn't manage to upgrade it to get 2 counts of media (based on their type)
Basically, get the folder details (name, etc) for all folders that belong to a user(fk_userID) and also, for each folder get the number of images and videos in it (as separate values).
The select would basically return:
folderName, count(images in folder), count(videos in folder), other folder details.
One obvious solution would be to just get all folders and then manually calculate the number of images/videos in them... but I would first like to try with a query.
Thank you,

Answer 1

Basically something like this:
SELECT
f.pk_folderID,
f.folderName,
VideoCount = COUNT(CASE m.MediaType WHEN 'Video' THEN 1 END),
ImageCount = COUNT(CASE m.MediaType WHEN 'Image' THEN 1 END)
FROM Folder f
LEFT JOIN FolderMedia fm ON f.pk_folderID = fm.fk_folderID
LEFT JOIN Media m ON fm.fk_media = m.pk_media
WHERE f.fk_userID = #UserID
GROUP BY
f.pk_folderID,
f.folderName
UPDATE (based on the additional request):
To include a sort of TOP 1 Media.Name into the result set, the above query could be changed like this:
SELECT
f.pk_folderID,
f.folderName,
VideoCount = COUNT(CASE m.MediaType WHEN 'Video' THEN 1 END),
ImageCount = COUNT(CASE m.MediaType WHEN 'Image' THEN 1 END),
MediaName = MAX(CASE fm.timestamp WHEN t.timestamp THEN m.Name END)
FROM Folder f
LEFT JOIN FolderMedia fm ON f.pk_folderID = fm.fk_folderID
LEFT JOIN Media m ON fm.fk_media = m.pk_media
LEFT JOIN (
SELECT
fk_folderID,
timestamp = MIN(timestamp)
FROM FolderMedia
GROUP BY fk_folderID
) t ON fm.fk_folderID = t.fk_folderID AND fm.timestamp = t.timestamp
WHERE f.fk_userID = #UserID
GROUP BY
f.pk_folderID,
f.folderName
In cases where minimal FolderMedia.timestamp values are not unique within their folders, the ultimate value of the corresponding Media.Name will be decided by its alphabetical sorting. In particular, the above query selects the last one of the set (with MAX()).

Answer 2

Get all data you need from Folders table left join it with FolderMedia and Media
use sum with case inside to count all videos and images.
SUM(CASE WHEN mediaTypeId = videoId THEN 1 ELSE 0 END) as videoCount

Answer 3

//select folderName ,count(case when Folders.pk_folderID then 1 else null end)
count(SELECT FolderMedia.fk_media from FolderMedia JOIN Media on fk_media=pk_media where image is not null) as nrImg
etc..

Answer 4

Here is a query with some example data. Hope it helps.
declare #Folders table (pk_folderID int, folderName varchar(32), fk_userID int)
declare #Media table (pk_media int, name varchar(50), type varchar(32))
declare #FolderMedia table (fk_folderID int, fk_media int)
insert into #Folders values (1, 'Folder1', 1000)
insert into #Folders values (2, 'Folder2', 1000)
insert into #Folders values (3, 'Folder1', 2000)
insert into #Folders values (4, 'Folder1', 2000)
insert into #Media values (1, 'graph.jpg', 'image')
insert into #Media values (2, 'timer.jpg', 'image')
insert into #Media values (3, 'timer1.jpg', 'image')
insert into #Media values (4, 'harry_potter.mpeg', 'video')
insert into #Media values (5, 'harry_potter1.mpeg', 'video')
insert into #Media values (6, 'harry_potter2.mpeg', 'video')
insert into #FolderMedia values (1, 1)
insert into #FolderMedia values (1, 3)
insert into #FolderMedia values (1, 6)
insert into #FolderMedia values (2, 2)
insert into #FolderMedia values (2, 4)
select folderName, fk_userID, imageData.imgCount, videoData.videoCount from
#Folders
left outer join
(
select fk_folderID, COUNT(*) as imgCount
from #FolderMedia
inner join #Media
on fk_media = pk_media
and type = 'image'
group by fk_folderID
) as imageData
on imageData.fk_folderID = pk_folderID
left outer join
(
select fk_folderID, COUNT(*) as videoCount
from #FolderMedia
inner join #Media
on fk_media = pk_media
and type = 'video'
group by fk_folderID
) as videoData
on videoData.fk_folderID = pk_folderID
where fk_userID = 1000