是否需要在這裏嵌套兩個COUNT？

Question

所以，我對於銷售門票的活動服務三個表：

Event(id) 
Ticket(id, venue_id, seller_id) 
Venue(id, event_id) 
Seller(id) 

而且我想檢測，每一個事件，我有多少賣家（1型）有有隻有售票（並且該票是相應事件）。像

Event_id; First_time_sellers 
2814;3 
3092;24 
124;1 
... 

我有兩個疑問這個企圖，都未能得到錯誤的結果

SELECT event_id, 
    COUNT(DISTINCT rookie_seller) 
FROM 
(SELECT event_id, 
    rookie_seller, 
    tickets 
FROM 
(SELECT DISTINCT event.id AS event_id, 
    seller.id AS rookie_seller, 
    COUNT(DISTINCT ticket.id) AS tickets 
FROM ticket 
JOIN venue ON ticket.venue_id = venue.id 
JOIN event ON venue.event_id = event.id 
JOIN seller ON ticket.seller_id = seller.id 
WHERE seller.type = 1 
AND ticket.isforsale = 1 
GROUP BY rookie_seller) a 
WHERE tickets = 1) b 
GROUP BY event_id 

和

SELECT event.id, 
    a.seller_id, 
    a.tickets 
FROM ticket 
JOIN (
    SELECT seller.id AS seller_id, 
    COUNT(DISTINCT ticket.id) AS tickets 
FROM ticket 
JOIN seller ON ticket.seller_id = seller.id 
WHERE seller.type = 1 
AND ticket.isforsale = 1 
GROUP BY seller_id) a ON ticket.seller_id = a.seller_id 
JOIN venue ON ticket.venue_id = venue.id 
JOIN event ON venue.event_id = event.id 
WHERE a.tickets = 1 

我真的不知道是什麼問題。加入應該沒問題，還有計數條件，對不對？

感謝您的任何忠告:)

Answer 1

你確實需要這樣一個子查詢。但你可以更簡單地做到這一點：

SELECT event_id, COUNT(*) 
FROM (SELECT s.id, v.event_id, COUNT(*) as numTickets 
     FROM ticket t JOIN 
      seller s 
      ON t.seller_id = s.id JOIN 
      venue v 
      ON t.venue_id = v.id 
     WHERE s.type = 1 AND t.isforsale = 1 
     GROUP BY s.id 
     HAVING COUNT(*) = 1 
    ) s 
GROUP BY event_id;