增加一個額外的條件，SQL查詢

Question

我想一個額外層添加到我的SQL查詢，看起來像這樣：

SELECT 
    COUNT(*) totalCount 
FROM 
    ts_room 
WHERE 
    NOT EXISTS (
    SELECT 1 
    FROM ts_roompref 
     JOIN ts_request 
     ON ts_roompref.request_id = ts_request.id 
     AND day_id = 1 
     AND period_id = 1 
    WHERE 
     ts_room.id = ts_roompref.room_id) 

我想它做的是檢查一排匹配request.id不存在於名爲ts_allocation的表中。這是我迄今爲止嘗試的，但它似乎並沒有工作：

SELECT 
    COUNT(*) totalCount 

FROM 
    ts_room 

WHERE 
    NOT EXISTS (
    SELECT 1 
    FROM ts_roompref 
     JOIN ts_request 
     ON ts_roompref.request_id = ts_request.id 
     AND day_id = 1 
     AND period_id = 1 
    WHERE 
     ts_room.id = ts_roompref.room_id) 

AND NOT EXISTS (
    SELECT 1 
    FROM ts_roompref 
     JOIN ts_allocation 
     ON ts_roompref.request_id = ts_allocation.request_id 
     AND ts_allocation.status = "Allocated" 
    WHERE 
     ts_room.id = ts_roompref.room_id) 
) 

任何想法？我在這裏包含了我的SQL小提琴：http://sqlfiddle.com/#!2/4540d/2

Answer 1

我認爲問題與使用別名有關：一旦我將別名添加到查詢表中，查詢就會運行並返回一些值（link to your modified sqlfiddle）：

SELECT COUNT(*) totalCount 
FROM ts_room rm 
WHERE 
NOT EXISTS (
    SELECT 1 
    FROM ts_roompref rp 
    JOIN ts_request rq ON rp.request_id = rq.id AND day_id = 1 AND period_id = 1 
    WHERE rm.id = rp.room_id) 
AND NOT EXISTS (
    SELECT 1 
    FROM ts_roompref rp 
    JOIN ts_allocation a ON rp.request_id = a.request_id AND a.status = "Allocated" 
    WHERE rm.id = rp.room_id)