SQL nested count query - mysql

Question

I have these tables:
Discussion
----------
DiscussionID (Primary Key)
Name
....
UserDiscussion
--------------
UserID (Primary Key)
DiscussionID (Primary Key)
Participated (Boolean)
Bookmarked (Boolean)
and I need to query 2 things:
All discussions where a certain user has participated
For every participated discussion I need the total count of users who bookmarked the discussion
Here is my current query:
SELECT d.DiscussionID, d.Name
FROM Discussion d LEFT JOIN
UserDiscussion ud ON ud.DiscussionID = d.DiscussionID
WHERE ud.UserID = 1 AND ud.Participated = true;
Sample data:
Discussion:
DiscussionID | Name |
---------------------
1 First
UserDiscussion:
UserID | DiscussionID | Participated | Bookmarked |
===================================================
1 1 1 1
4 1 1 0
Output should look like this:
Discussions: [
{
DiscussionID: 1,
Name: "First",
BookmarkCount: 1
}
]

Answer 1

SELECT
d.DiscussionID
,d.Name
,Participated = SUM(CASE WHEN CAST(ISNULL(b.Participated,0) = 1 THEN 1 ELSE 0 END)
,Bookmarked = SUM(CASE WHEN CAST(ISNULL(b.Bookmarked,0) = 1 THEN 1 ELSE 0 END)
FROM
Discussion d
INNER JOIN UserDiscussion ud
ON d.DiscussionID = ud.DiscussionID
AND ud.Participated = true;
LEFT JOIN UserDiscussion b
ON d.DiscussionId = b.DiscussionId
GROUP BY
d.DiscussionID
,d.Name

Answer 2

You could use a temp table to get a count of the bookmarks related to each discussion ID
select DiscussionID, count(Bookmarked) as 'Bookmarked'
into #Bookmarks
from UserDiscussion
group by DiscussionID
then, join it to the final table on DiscussionID and you can use the count as a column.
SELECT d.DiscussionID, d.Name, b.Bookmarked
FROM Discussion d LEFT JOIN
UserDiscussion ud ON ud.DiscussionID = d.DiscussionID
left join #Bookmarked b on ud.DiscussionID = b.DiscussionID
WHERE ud.UserID = 1 AND ud.Participated = true;

Answer 3

You can use a in clause with a subqyery ,, and count
SELECT a.DiscussionID, a.Name, b.count(*)
FROM discussion a
INNER JOIN UserDiscussion b
WHERE a.DiscussionID in (
SELECT d.DiscussionID
FROM Discussion d
INNER JOIN UserDiscussion ud ON ud.DiscussionID = d.DiscussionID
WHERE ud.UserID = 1 AND ud.Participated = true
)
AND b.Bookmarked = true;
group by a.DiscussionID, a.Name

Answer 4

One way is to write a view for number of times bookmarked
CREATE OR REPLACE VIEW v_times_bookmarked (
discussion_id,
times_bookmarked ) AS
SELECT discussion_id, count(*)
FROM userdiscussion
WHERE Bookmarked = true
GROUP BY discussion_id
Then in your main query, left join to the view.

Answer 5

sound like you have the 1st query the 2d should be like
SELECT DiscussionID, count(UserID)
FROM UserDiscussion
WHERE DiscussionID in (SELECT DiscussionID from UserDiscussion WHERE ud.UserID = 1 AND ud.Participated = true)
AND Bookmarked = true
GROUP BY DiscussionID;
then eventually you need to join them
With the posted correction:
SELECT d.DiscussionID, d.Name, BookmarkCount
FROM Discussion d
JOIN UserDiscussion ud ON ud.DiscussionID = d.DiscussionID
JOIN (
SELECT DiscussionID as DID, count(UserID) as BookmarkCount
FROM UserDiscussion
WHERE DiscussionID in (SELECT DiscussionID from UserDiscussion WHERE
ud.UserID = 1 AND ud.Participated = true)
AND Bookmarked = true
GROUP BY DiscussionID
) ON d.DiscussionID=DID;