语法与类似，MySQL中除外

我的查询需要执行以下操作：

  SELECT 
  c1.building,
  c1.room_number 
FROM
  time_slot AS t,
  section AS s,
  classroom AS c1 
WHERE c1.capacity > 30 
  AND s.semester = 'Fall' 
  AND s.year = '2009' 
  AND t.day = 'M' 
  AND t.start_hr < 12 EXCEPT 
  SELECT 
    c1.building,
    c1.room_number 
  FROM
    time_slot AS t,
    section AS s NATURAL 
    JOIN classroom AS c1 
  WHERE c1.capacity > 30 
    AND s.semester = 'Fall' 
    AND s.year = '2009' 
    AND t.day = 'M' 
    AND t.start_hr < 12 

---

它必须在2009年秋季学期的周一中午之前，返回教室桌子上所有未占用的建筑物名称和房间号。更改where语句无效，因为它会给我一个不同的结果。

时间段与分区和/或教室的关系如何？我很抱歉不清楚。教室建筑、房间号、容量分区课程号、课室号、学期号、年份号、建筑号、房间号、时间段号、时间段号、日期、开始时间、开始时间、开始时间、开始时间、开始时间、开始时间、开始时间、开始时间、结束时间、结束时间，结束，结束，结束。见加入。2.使用显式连接语法。3.在这一点上，一切都将变得清晰

SELECT 
  c1.building,
  c1.room_number 
FROM
  time_slot AS t,
  section AS s,
  classroom AS c1 
WHERE c1.capacity > 30 
  AND s.semester = 'Fall' 
  AND s.year = '2009' 
  AND t.day = 'M' 
  AND t.start_hr < 12 and ( c1.building,
  c1.room_number ) not in (
  SELECT 
    c1.building,
    c1.room_number 
  FROM
    time_slot AS t,
    section AS s NATURAL 
    JOIN classroom AS c1 
  WHERE c1.capacity > 30 
    AND s.semester = 'Fall' 
    AND s.year = '2009' 
    AND t.day = 'M' 
    AND t.start_hr < 12 )