难以理解基本的 sql 语句

Question

我卡在 sql 语句上，需要一些帮助。我是数据库和访问 2007 的新手，所以我不太了解所有语法，任何指导都将非常感谢

一些信息

Teacher = [CourseN, Quarter,TeacherName]
Course = [CourseN,CourseName, Nunit)
Section = [CourseN, Quarter , DayTime,  RoomN]/ Examples of DayTime: M2:00AM, 
W4:50PM, and T8:00PM. Note that DayTime is represented as a string.
Student = [studentName, CourseN, Quarter]

问题

13. List the CourseN and Quarter of every course taught by two 
different instructors in the same quarter ordered by the CourseN in descending order.

老师Table

CourseN Quarter TeacherName
1   Winter 2011 Karen Reed
1   Winter 2011 Sun     <--- cant add this one which i need to make it   work
2   Spring 2005 Salloum
3   Spring 2005 Karen Reed
4   Spring 2005 Salloum
5   Winter 2011 Sun

关于第二个的问题是它不允许我将重复的 courseN 放入我的数据库中 table 因为它是索引、主键或关系所以我不知道该怎么做，因为我无法输入它在我的 table

编辑: 我删除了第一个问题，因为我解决了，所以post

Answer 1

我想你需要这样的东西。

对于第一个查询，您需要按课程编号连接表 "Course" 和 "Section"，这是关键。现在，我认为您不需要在 dayTime 上进行任何字符串操作，因为您只关心聚合将保存的记录数。

对于第二个查询，您将需要再次按课程编号连接表 "Course" 和 "Teacher"。

这两个查询都应该使用 Group By 和 Having 子句，因为您需要在这两个查询中进行聚合，这取决于教师/每周会议的数量。

希望对您有所帮助。

drop table #Teacher
SELECT  *
into #Teacher
FROM    
(
    select 1 as CourseN, 1 as Quarter, 'Dan' as TeacherName
        union
    select 1 as CourseN, 1 as Quarter, 'Alex' as TeacherName
        union
    select 2 as CourseN, 1 as Quarter, 'Rob' as TeacherName
        union
    select 3 as CourseN, 2 as Quarter, 'Jim' as TeacherName
        union
    select 4 as CourseN, 3 as Quarter, 'Bob' as TeacherName
        union
    select 4 as CourseN, 3 as Quarter, 'Alice' as TeacherName
) a

drop table #Course
SELECT  *
into #Course
FROM    
(
select 1 as CourseN, 'English' as CourseName, 1 as Nunit
    UNION
select 2 as CourseN, 'Algebra' as CourseName, 1 as Nunit
    UNION
select 3 as CourseN, 'Math' as CourseName, 1 as Nunit
    UNION
select 4 as CourseN, 'Science' as CourseName, 1 as Nunit
) a


drop table #Section
SELECT  *
into #Section
FROM    
(
    select 1 as CourseN, 1 as Quarter, 'M2:00AM' as DayTime , 1 as RoomN
        UNION
    select 1 as CourseN, 1 as Quarter, 'W2:00AM' as DayTime , 1 as RoomN
        UNION
    select 2 as CourseN, 1 as Quarter, 'W2:00AM' as DayTime , 1 as RoomN
        UNION
    select 3 as CourseN, 2 as Quarter, 'W2:00AM' as DayTime , 1 as RoomN
        UNION
    select 3 as CourseN, 2 as Quarter, 'T2:00AM' as DayTime , 1 as RoomN
        UNION
    select 4 as CourseN, 3 as Quarter, 'T2:00AM' as DayTime , 1 as RoomN
) a


--List the CourseN, CourseName, and Quarter which meets or met at least  two times a week.
select a.CourseN , a.CourseName , b.Quarter --, COUNT(b.CourseN) NumOfWeeklyMeetings
from #Course a
    inner join #Section b
        on a.CourseN = b.CourseN
Where 1=1
GROUP BY a.CourseN , a.CourseName , b.Quarter
having COUNT(b.CourseN) > 1


--List the CourseN and Quarter of every course taught by two 
--different instructors in the same quarter ordered by the CourseN in descending order.
SELECT  a.CourseN , b.Quarter --, count(b.TeacherName) NumOfTeachers
FROM    #Course a
    inner join #Teacher b 
        on a.CourseN = b.CourseN
WHERE 1=1
group by a.CourseN , b.Quarter
having count(b.TeacherName) > 1

难以理解基本的 sql 语句

trouble understand basic sql statements

sql

database

ms-access