mysql - SQL WHERE 与乘法 JOIN 和 GROUP BY

Question

我正在尝试获得类(class)表重叠的教室，我的表格:类(class):

COURSE_ID    NAME
11           matematika
22           logika

时间表:

ID COURSE_ID ID_ROOM DAY HOUR
1   11  105 Mon 10am
2   11  105 Wen 10am

教室:

ID_ROOM LOCATION CAPACITY
105 A   20
205 B   10

我的sql是:

select class_room.ID_ROOM as crid, class_room.LOCATION, schedule.DAY as d, schedule.HOUR as h,  count(courses.COURSE_ID) as count 
  from schedule
  natural join class_room
  natural join courses
  group by crid, d, h
  order by count desc;

我得到:

crid LOCATION d h count
105 A   Mon 10am    3
105 A   Thu 10am    2
305 C   Mon 11am    1
105 A   Wen 10am    1
205 B   Wen 10am    1

但我只需要显示计数大于 1 的行。我试过了

select class_room.ID_ROOM as crid, class_room.LOCATION, schedule.DAY as d, schedule.HOUR as h,  count(courses.COURSE_ID) as count 
  from schedule
  natural join class_room
  natural join courses
  where count>1
  group by crid, d, h
  order by count desc;

但我收到 1054 错误如何解决？

Answer 1

不要使用where。使用拥有

select class_room.ID_ROOM as crid, class_room.LOCATION, schedule.DAY as d, schedule.HOUR as h,  count(courses.COURSE_ID) as count 
  from schedule
  natural join class_room
  natural join courses
  group by crid, d, h
  having count>1
  order by count desc;