標准答案

標准答案

2、查詢“生物”課程比“物理”課程成績高的所有學生的學號；

思路：

    獲取所有有生物課程的人（學號，成績） - 臨時表

    獲取所有有物理課程的人（學號，成績） - 臨時表

    根據【學號】連接兩個臨時表：

        學號  物理成績   生物成績

 

    然后再進行篩選

 

        select A.student_id,sw,ty from

 

        (select student_id,num as sw from score left join course on score.course_id = course.cid where course.cname = '生物') as A

 

        left join

 

        (select student_id,num  as ty from score left join course on score.course_id = course.cid where course.cname = '體育') as B

 

        on A.student_id = B.student_id where sw > if(isnull(ty),0,ty);

 

3、查詢平均成績大於60分的同學的學號和平均成績； 

    思路：

        根據學生分組，使用avg獲取平均值，通過having對avg進行篩選

 

        select student_id,avg(num) from score group by student_id having avg(num) > 60

 

4、查詢所有同學的學號、姓名、選課數、總成績；

 

    select score.student_id,sum(score.num),count(score.student_id),student.sname 

    from

        score left join student on score.student_id = student.sid   

    group by score.student_id

 

5、查詢姓“李”的老師的個數；

    select count(tid) from teacher where tname like '李%'

 

    select count(1) from (select tid from teacher where tname like '李%') as B

 

6、查詢沒學過“葉平”老師課的同學的學號、姓名；

    思路：

        先查到“李平老師”老師教的所有課ID

        獲取選過課的所有學生ID

        學生表中篩選

    select * from student where sid not in (

        select DISTINCT student_id from score where score.course_id in (

            select cid from course left join teacher on course.teacher_id = teacher.tid where tname = '李平老師'

        )

    )

 

7、查詢學過“001”並且也學過編號“002”課程的同學的學號、姓名；

    思路：

        先查到既選擇001又選擇002課程的所有同學

        根據學生進行分組，如果學生數量等於2表示，兩門均已選擇

 

    select student_id,sname from

 

    (select student_id,course_id from score where course_id = 1 or course_id = 2) as B

      

    left join student on B.student_id = student.sid group by student_id HAVING count(student_id) > 1

 

 

8、查詢學過“葉平”老師所教的所有課的同學的學號、姓名；

 

    同上，只不過將001和002變成 in (葉平老師的所有課)

 

9、查詢課程編號“002”的成績比課程編號“001”課程低的所有同學的學號、姓名；

    同第1題

 

 

10、查詢有課程成績小於60分的同學的學號、姓名；

         

    select sid,sname from student where sid in (

        select distinct student_id from score where num < 60

    )

 

11、查詢沒有學全所有課的同學的學號、姓名；

    思路：

        在分數表中根據學生進行分組，獲取每一個學生選課數量

        如果數量 == 總課程數量，表示已經選擇了所有課程

 

        select student_id,sname 

        from score left join student on score.student_id = student.sid 

        group by student_id HAVING count(course_id) = (select count(1) from course)

 

 

12、查詢至少有一門課與學號為“001”的同學所學相同的同學的學號和姓名；

    思路：

        獲取 001 同學選擇的所有課程

        獲取課程在其中的所有人以及所有課程

        根據學生篩選，獲取所有學生信息

        再與學生表連接，獲取姓名

 

        select student_id,sname, count(course_id) 

        from score left join student on score.student_id = student.sid

        where student_id != 1 and course_id in (select course_id from score where student_id = 1) group by student_id

 

13、查詢至少學過學號為“001”同學所有課的其他同學學號和姓名；

        先找到和001的學過的所有人

        然后個數 ＝ 001所有學科     ＝＝》 其他人可能選擇的更多

 

        select student_id,sname, count(course_id) 

        from score left join student on score.student_id = student.sid

        where student_id != 1 and course_id in (select course_id from score where student_id = 1) group by student_id having count(course_id) ＝ (select count(course_id) from score where student_id = 1)

 

14、查詢和“002”號的同學學習的課程完全相同的其他同學學號和姓名；

         

        個數相同

        002學過的也學過

 

        select student_id,sname from score left join student on score.student_id = student.sid where student_id in (

            select student_id from score  where student_id != 1 group by student_id HAVING count(course_id) = (select count(1) from score where student_id = 1)

        ) and course_id in (select course_id from score where student_id = 1) group by student_id HAVING count(course_id) = (select count(1) from score where student_id = 1)

 

 

15、刪除學習“葉平”老師課的score表記錄；

 

    delete from score where course_id in (

        select cid from course left join teacher on course.teacher_id = teacher.tid where teacher.name = '葉平'

    )

 

16、向SC表中插入一些記錄，這些記錄要求符合以下條件：①沒有上過編號“002”課程的同學學號；②插入“002”號課程的平均成績； 

    思路：

        由於insert 支持  

                inset into tb1(xx,xx) select x1,x2 from tb2;

        所有，獲取所有沒上過002課的所有人，獲取002的平均成績

 

    insert into score(student_id, course_id, num) select sid,2,(select avg(num) from score where course_id = 2) 

    from student where sid not in (

        select student_id from score where course_id = 2

    )

     

17、按平均成績從低到高 顯示所有學生的“語文”、“數學”、“英語”三門的課程成績，按如下形式顯示： 學生ID,語文,數學,英語,有效課程數,有效平均分；

    select sc.student_id,

        (select num from score left join course on score.course_id = course.cid where course.cname = "生物" and score.student_id=sc.student_id) as sy,

        (select num from score left join course on score.course_id = course.cid where course.cname = "物理" and score.student_id=sc.student_id) as wl,

        (select num from score left join course on score.course_id = course.cid where course.cname = "體育" and score.student_id=sc.student_id) as ty,

        count(sc.course_id),

        avg(sc.num)

    from score as sc

    group by student_id desc        

 

18、查詢各科成績最高和最低的分：以如下形式顯示：課程ID，最高分，最低分；

     

    select course_id, max(num) as max_num, min(num) as min_num from score group by course_id;

 

19、按各科平均成績從低到高和及格率的百分數從高到低順序；

    思路：case when .. then

    select course_id, avg(num) as avgnum,sum(case when score.num > 60 then 1 else 0 END)/count(1)*100 as percent from score group by course_id order by avgnum asc,percent desc;

 

20、課程平均分從高到低顯示（現實任課老師）；

 

    select avg(if(isnull(score.num),0,score.num)),teacher.tname from course 

    left join score on course.cid = score.course_id 

    left join teacher on course.teacher_id = teacher.tid

 

    group by score.course_id

 

 

21、查詢各科成績前三名的記錄:(不考慮成績並列情況) 

    select score.sid,score.course_id,score.num,T.first_num,T.second_num from score left join

    (

    select

        sid,

        (select num from score as s2 where s2.course_id = s1.course_id order by num desc limit 0,1) as first_num,

        (select num from score as s2 where s2.course_id = s1.course_id order by num desc limit 3,1) as second_num

    from

        score as s1

    ) as T

    on score.sid =T.sid

    where score.num <= T.first_num and score.num >= T.second_num

 

22、查詢每門課程被選修的學生數；

     

    select course_id, count(1) from score group by course_id;

 

23、查詢出只選修了一門課程的全部學生的學號和姓名；

    select student.sid, student.sname, count(1) from score

 

    left join student on score.student_id  = student.sid

 

     group by course_id having count(1) = 1

 

 

24、查詢男生、女生的人數；

    select * from

    (select count(1) as man from student where gender='男') as A ,

    (select count(1) as feman from student where gender='女') as B 

 

25、查詢姓“張”的學生名單；

    select sname from student where sname like '張%';

 

26、查詢同名同姓學生名單，並統計同名人數；

 

    select sname,count(1) as count from student group by sname;

 

27、查詢每門課程的平均成績，結果按平均成績升序排列，平均成績相同時，按課程號降序排列；

    select course_id,avg(if(isnull(num), 0 ,num)) as avg from score group by course_id order by avg     asc,course_id desc;

 

28、查詢平均成績大於85的所有學生的學號、姓名和平均成績；

 

    select student_id,sname, avg(if(isnull(num), 0 ,num)) from score left join student on score.student_id = student.sid group by student_id;

 

29、查詢課程名稱為“數學”，且分數低於60的學生姓名和分數；

 

    select student.sname,score.num from score 

    left join course on score.course_id = course.cid

    left join student on score.student_id = student.sid

    where score.num < 60 and course.cname = '生物'

 

30、查詢課程編號為003且課程成績在80分以上的學生的學號和姓名； 

    select * from score where score.student_id = 3 and score.num > 80

 

31、求選了課程的學生人數

 

    select count(distinct student_id) from score

 

    select count(c) from (

        select count(student_id) as c from score group by student_id) as A

 

32、查詢選修“楊艷”老師所授課程的學生中，成績最高的學生姓名及其成績；

     

    select sname,num from score 

    left join student on score.student_id = student.sid

    where score.course_id in (select course.cid from course left join teacher on course.teacher_id = teacher.tid where tname='張磊老師') order by num desc limit 1;

 

33、查詢各個課程及相應的選修人數；

    select course.cname,count(1) from score

    left join course on score.course_id = course.cid

    group by course_id;

 

 

34、查詢不同課程但成績相同的學生的學號、課程號、學生成績；

    select DISTINCT s1.course_id,s2.course_id,s1.num,s2.num from score as s1, score as s2 where s1.num = s2.num and s1.course_id != s2.course_id;

 

35、查詢每門課程成績最好的前兩名；

 

    select score.sid,score.course_id,score.num,T.first_num,T.second_num from score left join

    (

    select

        sid,

        (select num from score as s2 where s2.course_id = s1.course_id order by num desc limit 0,1) as first_num,

        (select num from score as s2 where s2.course_id = s1.course_id order by num desc limit 1,1) as second_num

    from

        score as s1

    ) as T

    on score.sid =T.sid

    where score.num <= T.first_num and score.num >= T.second_num

 

36、檢索至少選修兩門課程的學生學號；

    select student_id from score group by student_id having count(student_id) > 1

 

37、查詢全部學生都選修的課程的課程號和課程名；

    select course_id,count(1) from score group by course_id having count(1) = (select count(1) from student);

 

38、查詢沒學過“葉平”老師講授的任一門課程的學生姓名；

    select student_id,student.sname from score 

    left join student on score.student_id = student.sid

    where score.course_id not in (

        select cid from course left join teacher on course.teacher_id = teacher.tid where tname = '張磊老師'

    ) 

    group by student_id

 

39、查詢兩門以上不及格課程的同學的學號及其平均成績；

 

    select student_id,count(1) from score where num < 60 group by student_id having count(1) > 2

 

40、檢索“004”課程分數小於60，按分數降序排列的同學學號；

    select student_id from score where num< 60 and course_id = 4 order by num desc;

 

41、刪除“002”同學的“001”課程的成績；

    delete from score where course_id = 1 and student_id = 2