mysql - 向 SQL 查询添加额外条件

Question

我正在尝试向我的 SQL 查询添加一个额外的层，如下所示：

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)

我想做的是检查匹配 request.id 的行在名为 ts_allocation 的表中是否不存在。到目前为止，这是我尝试过的，但似乎没有用：

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)
  )

有任何想法吗？我在这里包含了我的 SQL Fiddle：http ://sqlfiddle.com/#!2/4540d/2

Answer 1

我认为问题与别名的使用有关：一旦我将别名添加到查询表中，查询就会运行并返回一些值（链接到您修改的 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)