Question

我正在努力让课堂上有重叠的课程安排，我的课程：课程：

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

class_room：

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;

我得到了：

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超过1的行。我试过

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;

但我得到1054错误怎么解决这个问题？

Answer 1

请勿使用where。使用having

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;

Answer 2

删除count > 1，然后添加having count(courses.COURSE_ID) > 1

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SQL WHERE与乘法JOIN和GROUP BY

2 个答案: