MySQL練習題參考答案

 

MySQL練習題參考答案

二、查詢「生物」課程比「物理」課程成績高的全部學生的學號；
思路：
    獲取全部有生物課程的人（學號，成績） - 臨時表
    獲取全部有物理課程的人（學號，成績） - 臨時表
    根據【學號】鏈接兩個臨時表：
        學號  物理成績   生物成績
 
    而後再進行篩選
 
        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);
 
三、查詢平均成績大於60分的同窗的學號和平均成績；
    思路：
        根據學生分組，使用avg獲取平均值，經過having對avg進行篩選
 
        select student_id,avg(num) from score group by student_id having avg(num) > 60
 
四、查詢全部同窗的學號、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
 
五、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
 
六、查詢沒學過「葉平」老師課的同窗的學號、姓名；
    思路：
        先查到「李平老師」老師教的全部課ID
        獲取選過課的全部學生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'
        )
    )
 
七、查詢學過「001」而且也學過編號「002」課程的同窗的學號、姓名；
    思路：
        先查到既選擇001又選擇002課程的全部同窗
        根據學生進行分組，若是學生數量等於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
 
 
八、查詢學過「葉平」老師所教的全部課的同窗的學號、姓名；
 
    同上，只不過將001和002變成 in (葉平老師的全部課)
 
九、查詢課程編號「002」的成績比課程編號「001」課程低的全部同窗的學號、姓名；
    同第1題
 
 
十、查詢有課程成績小於60分的同窗的學號、姓名；
         
    select sid,sname from student where sid in (
        select distinct student_id from score where num < 60
    )
 
十一、查詢沒有學全全部課的同窗的學號、姓名；
    思路：
        在分數表中根據學生進行分組，獲取每個學生選課數量
        若是數量 == 總課程數量，表示已經選擇了全部課程
 
        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)
 
 
十二、查詢至少有一門課與學號爲「001」的同窗所學相同的同窗的學號和姓名；
    思路：
        獲取 001 同窗選擇的全部課程
        獲取課程在其中的全部人以及全部課程
        根據學生篩選，獲取全部學生信息
        再與學生錶鏈接，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
 
1三、查詢至少學過學號爲「001」同窗全部課的其餘同窗學號和姓名；
        先找到和001的學過的全部人
        而後個數 ＝ 001全部學科     ＝＝》 其餘人可能選擇的更多
 
        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)
 
1四、查詢和「002」號的同窗學習的課程徹底相同的其餘同窗學號和姓名；
         
        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)
 
 
1五、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'
    )
 
1六、向SC表中插入一些記錄，這些記錄要求符合如下條件：①沒有上過編號「002」課程的同窗學號；②插入「002」號課程的平均成績；
    思路：
        因爲insert 支持 
                inset into tb1(xx,xx) select x1,x2 from tb2;
        全部，獲取全部沒上過002課的全部人，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
    )
     
1七、按平均成績從低到高 顯示全部學生的「語文」、「數學」、「英語」三門的課程成績，按以下形式顯示： 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        
 
1八、查詢各科成績最高和最低的分：以以下形式顯示：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;
 
1九、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
 
 
2一、查詢各科成績前三名的記錄:(不考慮成績並列狀況)
    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
 
2二、查詢每門課程被選修的學生數；
     
    select course_id, count(1) from score group by course_id;
 
2三、查詢出只選修了一門課程的所有學生的學號和姓名；
    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
 
 
2四、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
 
2五、查詢姓「張」的學生名單；
    select sname from student where sname like '張%';
 
2六、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;
 
2七、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;
 
2八、查詢平均成績大於85的全部學生的學號、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;
 
2九、查詢課程名稱爲「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、查詢課程編號爲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
 
3一、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
 
3二、查詢選修「楊豔」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;
 
3三、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;
 
 
3四、查詢不一樣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;
 
3五、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
 
3六、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
 
3七、查詢所有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);
 
3八、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
 
3九、查詢兩門以上不及格課程的同窗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窗學號；
    select student_id from score where num< 60 and course_id = 4 order by num desc;
 
4一、刪除「002」同窗的「001」課程的成績；
    delete from score where course_id = 1 and student_id = 2