Multiple COUNT(*) with join - sql-server

Question

I have to COUNT some rows from multiple tables. Before I can do multiple COUNT I will have to subselect. The problem here is that I need to JOIN some values in order to get the right result.
SELECT
sponsor.Name As SponsorName,
COUNT(participants.[Table]) AS ParticipantCount,
( SELECT
COUNT(guestcards.[Table])
FROM
guestcards
WHERE
guestcards.EventID = #EventID
AND
guestcards.[Table] = #Table
AND
guestcards.SponsorID = participants.SponsorID
-- Here lies the problem.
-- I will need to check up on another value to ensure I get the right rows, but participants.SponsorID is not here because of no join :-(
) AS GuestParticipantCount
FROM
participants
LEFT JOIN
sponsor
ON
sponsor.ID = participants.SponsorID
WHERE
participants.EventID = #EventID
AND
participants.[Table] = #Table
GROUP BY
sponsor.Name
Guestcards table holds: sponsorid, eventid, tablename
Participantstable holds: sponsorid, eventid, tablename
Sponsor table holds: id, name
I need to count how many "Participants" there are and how many "Guestcards" that in a particulary event. These participants have a table (where they should sit) and so does the guestcards. I need to check up on if its the same "table" where they sit.
So I need to count how many are sitting at table "A1" or table "A2" etc.
The result I am after is like:
"Sponsor Name has 5 participants and 3 guestcards. They sit on A1"
I hope I made my self clear

Answer 1

Here's exact equivalent of you query (grouping on sponsor.Name):
SELECT sponsor.name,
COALESCE(SUM(participantCount), 0),
COALESCE(SUM(guestcardsCount), 0)
FROM (
SELECT sponsorId, COUNT(*) AS participantCount
FROM participants
WHERE eventId = #eventId
AND [table] = #table
GROUP BY
sponsorId
) p
FULL JOIN
(
SELECT sponsorId, COUNT(*) AS guestcardsCount
FROM guestdcards
WHERE eventId = #eventId
AND [table] = #table
GROUP BY
sponsorId
) g
ON g.sponsorId = p.sponsorId
FULL JOIN
sponsor s
ON s.id = COALESCE(p.sponsorId, g.sponsorId)
GROUP BY
s.sponsorName
However, I believe you want something more simple:
SELECT sponsorName, participantCount, guestcardsCount
FROM sponsor s
CROSS APLLY
(
SELECT COUNT(*) AS participantCount
FROM participants
WHERE sponsorId = s.id
AND eventId = #eventId
AND [table] = #table
) p
CROSS APLLY
(
SELECT COUNT(*) AS guestcardsCount
FROM guestdcards
WHERE sponsorId = s.id
AND eventId = #eventId
AND [table] = #table
) g
Update:
SELECT sponsor.name,
COALESCE(participantCount, 0),
COALESCE(guestcardsCount, 0)
FROM (
SELECT sponsorId, COUNT(*) AS participantCount
FROM participants
WHERE eventId = #eventId
AND [table] = #table
GROUP BY
sponsorId
) p
FULL JOIN
(
SELECT sponsorId, COUNT(*) AS guestcardsCount
FROM guestdcards
WHERE eventId = #eventId
AND [table] = #table
GROUP BY
sponsorId
) g
ON g.sponsorId = p.sponsorId
JOIN sponsor s
ON s.id = COALESCE(p.sponsorId, g.sponsorId)