MySQL基础练习题

数据表介绍

--1.学生表
Student(SId,Sname,Sage,Ssex)
--SId 学生编号,Sname 学生姓名,Sage 出生年月,Ssex 学生性别

--2.课程表
Course(CId,Cname,TId)
--CId 课程编号,Cname 课程名称,TId 教师编号

--3.教师表
Teacher(TId,Tname)
--TId 教师编号,Tname 教师姓名

--4.成绩表
SC(SId,CId,score)
--SId 学生编号,CId 课程编号,score 分数

学生表 Student

create table Student(SId varchar(10),Sname varchar(10),Sage datetime,Ssex varchar(10));

insert into Student values('01' , '赵雷' , '1990-01-01' , '男');

insert into Student values('02' , '钱电' , '1990-12-21' , '男');

insert into Student values('03' , '孙风' , '1990-12-20' , '男');

insert into Student values('04' , '李云' , '1990-12-06' , '男');

insert into Student values('05' , '周梅' , '1991-12-01' , '女');

insert into Student values('06' , '吴兰' , '1992-01-01' , '女');

insert into Student values('07' , '郑竹' , '1989-01-01' , '女');

insert into Student values('09' , '张三' , '2017-12-20' , '女');

insert into Student values('10' , '李四' , '2017-12-25' , '女');

insert into Student values('11' , '李四' , '2012-06-06' , '女');

insert into Student values('12' , '赵六' , '2013-06-13' , '女');

insert into Student values('13' , '孙七' , '2014-06-01' , '女');

科目表 Course

create table Course(CId varchar(10),Cname nvarchar(10),TId varchar(10));

insert into Course values('01' , '语文' , '02');

insert into Course values('02' , '数学' , '01');

insert into Course values('03' , '英语' , '03');

教师表 Teacher

create table Teacher(TId varchar(10),Tname varchar(10));

insert into Teacher values('01' , '张三');

insert into Teacher values('02' , '李四');

insert into Teacher values('03' , '王五');

成绩表 SC

create table SC(SId varchar(10),CId varchar(10),score decimal(18,1));

insert into SC values('01' , '01' , 80);

insert into SC values('01' , '02' , 90);

insert into SC values('01' , '03' , 99);

insert into SC values('02' , '01' , 70);

insert into SC values('02' , '02' , 60);

insert into SC values('02' , '03' , 80);

insert into SC values('03' , '01' , 80);

insert into SC values('03' , '02' , 80);

insert into SC values('03' , '03' , 80);

insert into SC values('04' , '01' , 50);

insert into SC values('04' , '02' , 30);

insert into SC values('04' , '03' , 20);

insert into SC values('05' , '01' , 76);

insert into SC values('05' , '02' , 87);

insert into SC values('06' , '01' , 31);

insert into SC values('06' , '03' , 34);

insert into SC values('07' , '02' , 89);

insert into SC values('07' , '03' , 98);

1.查询" 01 "课程比" 02 "课程成绩高的学生的信息及课程分数

select SId,CId,score from sc where CId=1;    //查出01课程的学生，作为b1
select SId,CId,score from sc where CId=2;    //b2
 
select distinct b1.SId,b1.score from (select SId,CId,score from sc where CId=1) b1, (select SId,CId,score from sc where CId=2) b2 where b1.score>b2.score;   //查出01课程分数比02课程高的人，b3
 
mysql> select st.*,b3.score from student st inner join (select distinct b1.SId,b1.score from (select SId,CId,score from sc where CId=1) b1, (select SId,CId,score from sc where CId=2) b2 where b1.score>b2.score) b3 on(st.SId=b3.SId);
+------+--------+---------------------+------+-------+
| SId  | Sname  | Sage                | Ssex | score |
+------+--------+---------------------+------+-------+
| 01   | 赵雷   | 1990-01-01 00:00:00 | 男   |  80.0 |
| 02   | 钱电   | 1990-12-21 00:00:00 | 男   |  70.0 |
| 03   | 孙风   | 1990-12-20 00:00:00 | 男   |  80.0 |
| 04   | 李云   | 1990-12-06 00:00:00 | 男   |  50.0 |
| 05   | 周梅   | 1991-12-01 00:00:00 | 女   |  76.0 |
| 06   | 吴兰   | 1992-01-01 00:00:00 | 女   |  31.0 |
+------+--------+---------------------+------+-------+
6 rows in set (0.01 sec)    //将b3查出的表和student表关联查询得出学生的信息
2.查询同时存在" 01 "课程和" 02 "课程的情况

select * from sc where CId=1;  //查询课程1
select * from sc where CId=2;  //查询课程2
 
mysql> select * from (select * from sc where CId=1) b1,(select * from sc where CId=2) b2 where b1.SId=b2.SId;
+------+------+-------+------+------+-------+
| SId  | CId  | score | SId  | CId  | score |
+------+------+-------+------+------+-------+
| 01   | 01   |  80.0 | 01   | 02   |  90.0 |
| 02   | 01   |  70.0 | 02   | 02   |  60.0 |
| 03   | 01   |  80.0 | 03   | 02   |  80.0 |
| 04   | 01   |  50.0 | 04   | 02   |  30.0 |
| 05   | 01   |  76.0 | 05   | 02   |  87.0 |
+------+------+-------+------+------+-------+
5 rows in set (0.01 sec)
//联合两张表，查询课程1，2都有的人
3.查询存在" 01 "课程但可能不存在" 02 "课程的情况(不存在时显示为 null )

mysql> select * from (select * from sc where CId=1) b1 left join (select * from sc where CId=2) b2 on(b1.SId=b2.SId);
+------+------+-------+------+------+-------+
| SId  | CId  | score | SId  | CId  | score |
+------+------+-------+------+------+-------+
| 01   | 01   |  80.0 | 01   | 02   |  90.0 |
| 02   | 01   |  70.0 | 02   | 02   |  60.0 |
| 03   | 01   |  80.0 | 03   | 02   |  80.0 |
| 04   | 01   |  50.0 | 04   | 02   |  30.0 |
| 05   | 01   |  76.0 | 05   | 02   |  87.0 |
| 06   | 01   |  31.0 | NULL | NULL |  NULL |
+------+------+-------+------+------+-------+
6 rows in set (0.00 sec)
4.查询不存在" 01 "课程但存在" 02 "课程的情况

mysql> select * from sc where SId not in(select SId from sc where sc.CId=1)  and sc.CId=2;
+------+------+-------+
| SId  | CId  | score |
+------+------+-------+
| 07   | 02   |  89.0 |
+------+------+-------+
1 row in set (0.00 sec)
5.查询平均成绩大于等于 60 分的同学的学生编号和学生姓名和平均成绩

mysql> select st.sid,st.sname,b1.avg
    -> from student st,(select SId,avg(score) avg from sc group by SId having  avg(score)>60) b1
    -> where st.sid=b1.sid;
+------+--------+----------+
| sid  | sname  | avg      |
+------+--------+----------+
| 01   | 赵雷   | 89.66667 |
| 02   | 钱电   | 70.00000 |
| 03   | 孙风   | 80.00000 |
| 05   | 周梅   | 81.50000 |
| 07   | 郑竹   | 93.50000 |
+------+--------+----------+
5 rows in set (0.00 sec)
6.查询在 SC 表存在成绩的学生信息

mysql> select distinct st.* from student st,sc where st.sid=sc.sid;
+------+--------+---------------------+------+
| SId  | Sname  | Sage                | Ssex |
+------+--------+---------------------+------+
| 01   | 赵雷   | 1990-01-01 00:00:00 | 男   |
| 02   | 钱电   | 1990-12-21 00:00:00 | 男   |
| 03   | 孙风   | 1990-12-20 00:00:00 | 男   |
| 04   | 李云   | 1990-12-06 00:00:00 | 男   |
| 05   | 周梅   | 1991-12-01 00:00:00 | 女   |
| 06   | 吴兰   | 1992-01-01 00:00:00 | 女   |
| 07   | 郑竹   | 1989-01-01 00:00:00 | 女   |
+------+--------+---------------------+------+
7 rows in set (0.00 sec)
7.查询所有同学的学生编号、学生姓名、选课总数、所有课程的总成绩(没成绩的显示为 null )

mysql> select st.sid,st.sname,b1.选课数,b1.总成绩
    -> from (select student.sid,student.sname from student) st
    -> left join (select sid,count(sid) 选课数,sum(score) 总成绩 from sc group by sid) b1
    -> on(st.sid=b1.sid);
+------+--------+-----------+-----------+
| sid  | sname  | 选课数    | 总成绩    |
+------+--------+-----------+-----------+
| 01   | 赵雷   |         3 |     269.0 |
| 02   | 钱电   |         3 |     210.0 |
| 03   | 孙风   |         3 |     240.0 |
| 04   | 李云   |         3 |     100.0 |
| 05   | 周梅   |         2 |     163.0 |
| 06   | 吴兰   |         2 |      65.0 |
| 07   | 郑竹   |         2 |     187.0 |
| 09   | 张三   |      NULL |      NULL |
| 10   | 李四   |      NULL |      NULL |
| 11   | 李四   |      NULL |      NULL |
| 12   | 赵六   |      NULL |      NULL |
| 13   | 孙七   |      NULL |      NULL |
+------+--------+-----------+-----------+
12 rows in set (0.00 sec)

8.查有成绩的学生信息

mysql> select * from student where student.sid in (select sc.sid from sc);
+------+--------+---------------------+------+
| SId  | Sname  | Sage                | Ssex |
+------+--------+---------------------+------+
| 01   | 赵雷   | 1990-01-01 00:00:00 | 男   |
| 02   | 钱电   | 1990-12-21 00:00:00 | 男   |
| 03   | 孙风   | 1990-12-20 00:00:00 | 男   |
| 04   | 李云   | 1990-12-06 00:00:00 | 男   |
| 05   | 周梅   | 1991-12-01 00:00:00 | 女   |
| 06   | 吴兰   | 1992-01-01 00:00:00 | 女   |
| 07   | 郑竹   | 1989-01-01 00:00:00 | 女   |
+------+--------+---------------------+------+
7 rows in set (0.00 sec)
9.查询「李」姓老师的数量

mysql> select count(tname) from teacher where tname like '李%';
+--------------+
| count(tname) |
+--------------+
|            1 |
+--------------+
1 row in set (0.00 sec)
10.查询学过「张三」老师授课的同学的信息

mysql> select st.* from student st,
    -> (select sc.sid
    -> from sc,(select CId from course where tid=(select tid from teacher where tname='张三')) b1
    -> where sc.cid=b1.cid) b2
    -> where st.sid=b2.sid;
+------+--------+---------------------+------+
| SId  | Sname  | Sage                | Ssex |
+------+--------+---------------------+------+
| 01   | 赵雷   | 1990-01-01 00:00:00 | 男   |
| 02   | 钱电   | 1990-12-21 00:00:00 | 男   |
| 03   | 孙风   | 1990-12-20 00:00:00 | 男   |
| 04   | 李云   | 1990-12-06 00:00:00 | 男   |
| 05   | 周梅   | 1991-12-01 00:00:00 | 女   |
| 07   | 郑竹   | 1989-01-01 00:00:00 | 女   |
+------+--------+---------------------+------+
6 rows in set (0.00 sec)

11.查询没有学全所有课程的同学的信息

mysql> select st.* from student st
    -> where st.sid not in
    -> (select sc.sid
    -> from sc group by sc.sid
    -> having count(sc.cid)=(select count(cid) from course));
+------+--------+---------------------+------+
| SId  | Sname  | Sage                | Ssex |
+------+--------+---------------------+------+
| 05   | 周梅   | 1991-12-01 00:00:00 | 女   |
| 06   | 吴兰   | 1992-01-01 00:00:00 | 女   |
| 07   | 郑竹   | 1989-01-01 00:00:00 | 女   |
| 09   | 张三   | 2017-12-20 00:00:00 | 女   |
| 10   | 李四   | 2017-12-25 00:00:00 | 女   |
| 11   | 李四   | 2012-06-06 00:00:00 | 女   |
| 12   | 赵六   | 2013-06-13 00:00:00 | 女   |
| 13   | 孙七   | 2014-06-01 00:00:00 | 女   |
+------+--------+---------------------+------+
8 rows in set (0.00 sec)

12.查询至少有一门课与学号为" 01 "的同学所学相同的同学的信息

mysql> select st.* from
    -> student st,
    -> (select distinct sid from sc where sc.cid in((select cid from sc where sid=1))) b1
    -> where st.sid=b1.sid;
+------+--------+---------------------+------+
| SId  | Sname  | Sage                | Ssex |
+------+--------+---------------------+------+
| 01   | 赵雷   | 1990-01-01 00:00:00 | 男   |
| 02   | 钱电   | 1990-12-21 00:00:00 | 男   |
| 03   | 孙风   | 1990-12-20 00:00:00 | 男   |
| 04   | 李云   | 1990-12-06 00:00:00 | 男   |
| 05   | 周梅   | 1991-12-01 00:00:00 | 女   |
| 06   | 吴兰   | 1992-01-01 00:00:00 | 女   |
| 07   | 郑竹   | 1989-01-01 00:00:00 | 女   |
+------+--------+---------------------+------+
7 rows in set (0.00 sec)

13.查询和" 01 "号的同学学习的课程 完全相同的其他同学的信息

mysql> select st.* from student st,
    -> (select sid from
    -> (select count(cid) 选课数 from sc where sid=1) b1,
    -> (select sid,count(cid) 选课数 from sc group by sid) b2
    -> where b1.选课数=b2.选课数) b3
    -> where st.sid=b3.sid;
+------+--------+---------------------+------+
| SId  | Sname  | Sage                | Ssex |
+------+--------+---------------------+------+
| 01   | 赵雷   | 1990-01-01 00:00:00 | 男   |
| 02   | 钱电   | 1990-12-21 00:00:00 | 男   |
| 03   | 孙风   | 1990-12-20 00:00:00 | 男   |
| 04   | 李云   | 1990-12-06 00:00:00 | 男   |
+------+--------+---------------------+------+
4 rows in set (0.00 sec)
14.查询没学过"张三"老师讲授的任一门课程的学生姓名

mysql> select * from student where student.sid not
    -> in(select sc.sid from sc where sc.cid
    -> in(select cid from course co,
    -> (select tid from teacher where tname='张三') b1
    -> where co.tid=b1.tid));
+------+--------+---------------------+------+
| SId  | Sname  | Sage                | Ssex |
+------+--------+---------------------+------+
| 06   | 吴兰   | 1992-01-01 00:00:00 | 女   |
| 09   | 张三   | 2017-12-20 00:00:00 | 女   |
| 10   | 李四   | 2017-12-25 00:00:00 | 女   |
| 11   | 李四   | 2012-06-06 00:00:00 | 女   |
| 12   | 赵六   | 2013-06-13 00:00:00 | 女   |
| 13   | 孙七   | 2014-06-01 00:00:00 | 女   |
+------+--------+---------------------+------+
6 rows in set (0.00 sec)

15.查询两门及其以上不及格课程的同学的学号，姓名及其平均成绩

mysql> select st.sid,st.sname,b1.avg from
    -> student st,
    -> (select sid,avg(score) avg from sc where score<60 group by sid having count(score)>1) b1
    -> where st.sid=b1.sid;
+------+--------+----------+
| sid  | sname  | avg      |
+------+--------+----------+
| 04   | 李云   | 33.33333 |
| 06   | 吴兰   | 32.50000 |
+------+--------+----------+
2 rows in set (0.00 sec)
16.检索" 01 "课程分数小于 60，按分数降序排列的学生信息

mysql> select st.*,b1.score from student st,
    -> (select sid,score from sc where cid=1 and score<60) b1
    -> where st.sid=b1.sid
    -> order by b1.score desc;
+------+--------+---------------------+------+-------+
| SId  | Sname  | Sage                | Ssex | score |
+------+--------+---------------------+------+-------+
| 04   | 李云   | 1990-12-06 00:00:00 | 男   |  50.0 |
| 06   | 吴兰   | 1992-01-01 00:00:00 | 女   |  31.0 |
+------+--------+---------------------+------+-------+
2 rows in set (0.00 sec)
17.按平均成绩从高到低显示所有学生的所有课程的成绩以及平均成绩

mysql> select sc.sid,sc.cid,b1.avg from sc
    -> left join
    -> (select sid,avg(score) avg from sc group by sid) b1
    -> on sc.sid=b1.sid
    -> order by avg desc;
+------+------+----------+
| sid  | cid  | avg      |
+------+------+----------+
| 07   | 02   | 93.50000 |
| 07   | 03   | 93.50000 |
| 01   | 01   | 89.66667 |
| 01   | 02   | 89.66667 |
| 01   | 03   | 89.66667 |
| 05   | 01   | 81.50000 |
| 05   | 02   | 81.50000 |
| 03   | 01   | 80.00000 |
| 03   | 02   | 80.00000 |
| 03   | 03   | 80.00000 |
| 02   | 01   | 70.00000 |
| 02   | 02   | 70.00000 |
| 02   | 03   | 70.00000 |
| 04   | 01   | 33.33333 |
| 04   | 02   | 33.33333 |
| 04   | 03   | 33.33333 |
| 06   | 01   | 32.50000 |
| 06   | 03   | 32.50000 |
+------+------+----------+
18 rows in set (0.00 sec)

18.查询各科成绩最高分、最低分和平均分：以如下形式显示：课程 ID，课程 name，最高分，最低分，平均分，及格率，中等率，优良率，优秀率，及格为>=60，中等为：70-80，优良为：80-90，优秀为：>=90，要求输出课程号和选修人数，查询结果按人数降序排列，若人数相同，按课程号升序排列

mysql> select sc.cid,
    -> max(sc.score) 最高分,
    -> min(sc.score) 最低分,
    -> avg(sc.score) 平均分,
    -> count(*) 参选人数,
    -> sum(case when sc.score>=60 then 1 else 0 end)/count(*) 及格率,
    -> sum(case when sc.score>=70 and sc.score<80 then 1 else 0 end)/count(*) 中等率,
    -> sum(case when sc.score>=80 and sc.score<90 then 1 else 0 end)/count(*) 优良率,
    -> sum(case when sc.score>=90 then 1 else 0 end)/count(*) 优秀率
    -> from sc
    -> group by sc.cid
    -> order by count(*) desc,sc.cid asc;
+------+-----------+-----------+-----------+--------------+-----------+-----------+-----------+-----------+
| cid  | 最高分    | 最低分    | 平均分    | 参选人数     | 及格率    | 中等率    | 优良率    | 优秀率    |
+------+-----------+-----------+-----------+--------------+-----------+-----------+-----------+-----------+
| 01   |      80.0 |      31.0 |  64.50000 |            6 |    0.6667 |    0.3333 |    0.3333 |    0.0000 |
| 02   |      90.0 |      30.0 |  72.66667 |            6 |    0.8333 |    0.0000 |    0.5000 |    0.1667 |
| 03   |      99.0 |      20.0 |  68.50000 |            6 |    0.6667 |    0.0000 |    0.3333 |    0.3333 |
+------+-----------+-----------+-----------+--------------+-----------+-----------+-----------+-----------+
3 rows in set (0.00 sec)

19.按各科成绩进行排序，并显示排名， Score 重复时保留名次空缺

mysql> select a.cid, a.sid, a.score, count(b.score)+1  an
    -> from sc as a
    -> left join sc as b
    -> on a.score     -> group by a.cid, a.sid,a.score
    -> order by a.cid, an aSC;
+------+------+-------+----+
| cid  | sid  | score | an |
+------+------+-------+----+
| 01   | 01   |  80.0 |  1 |
| 01   | 03   |  80.0 |  1 |
| 01   | 05   |  76.0 |  3 |
| 01   | 02   |  70.0 |  4 |
| 01   | 04   |  50.0 |  5 |
| 01   | 06   |  31.0 |  6 |
| 02   | 01   |  90.0 |  1 |
| 02   | 07   |  89.0 |  2 |
| 02   | 05   |  87.0 |  3 |
| 02   | 03   |  80.0 |  4 |
| 02   | 02   |  60.0 |  5 |
| 02   | 04   |  30.0 |  6 |
| 03   | 01   |  99.0 |  1 |
| 03   | 07   |  98.0 |  2 |
| 03   | 02   |  80.0 |  3 |
| 03   | 03   |  80.0 |  3 |
| 03   | 06   |  34.0 |  5 |
| 03   | 04   |  20.0 |  6 |
+------+------+-------+----+
18 rows in set (0.00 sec)

22. 查询学生的总成绩，并进行排名，总分重复时不保留名次空缺

mysql> select a.sid,total,@crank:=@crank+1 an from(
    -> select sc.sid, sum(sc.score)  total from sc
    -> group by sc.sid order by total desc) a;
+------+-------+------+
| sid  | total | an   |
+------+-------+------+
| 01   | 269.0 |    1 |
| 03   | 240.0 |    2 |
| 02   | 210.0 |    3 |
| 07   | 187.0 |    4 |
| 05   | 163.0 |    5 |
| 04   | 100.0 |    6 |
| 06   |  65.0 |    7 |
+------+-------+------+
7 rows in set, 1 warning (0.00 sec)
23.统计各科成绩各分数段人数：课程编号，课程名称，[100-85]，[85-70]，[70-60]，[60-0] 及所占百分比

24.查询各科成绩前三名的记录

mysql> select * from sc
    -> where (
    -> select count(*) from sc as a
    -> where sc.cid = a.cid and sc.score     -> )< 3
    -> order by cid asc, sc.score desc;
+------+------+-------+
| SId  | CId  | score |
+------+------+-------+
| 01   | 01   |  80.0 |
| 03   | 01   |  80.0 |
| 05   | 01   |  76.0 |
| 01   | 02   |  90.0 |
| 07   | 02   |  89.0 |
| 05   | 02   |  87.0 |
| 01   | 03   |  99.0 |
| 07   | 03   |  98.0 |
| 02   | 03   |  80.0 |
| 03   | 03   |  80.0 |
+------+------+-------+

25.查询每门课程被选修的学生数

mysql> select cid,count(sid) from sc group by cid;
+------+------------+
| cid  | count(sid) |
+------+------------+
| 01   |          6 |
| 02   |          6 |
| 03   |          6 |
+------+------------+
3 rows in set (0.00 sec)
26.查询出只选修两门课程的学生学号和姓名

mysql> select distinct st.sid,st.sname from student st inner join
    -> (select sid,count(cid) 选课数 from sc group by sid having 选课数=2) b1
    -> on(st.sid=b1.sid);
+------+--------+
| sid  | sname  |
+------+--------+
| 05   | 周梅   |
| 06   | 吴兰   |
| 07   | 郑竹   |
+------+--------+
3 rows in set (0.00 sec)
27.查询男生、女生人数

mysql> select ssex,count(*) from student group by ssex;
+------+----------+
| ssex | count(*) |
+------+----------+
| 男   |        4 |
| 女   |        8 |
+------+----------+
2 rows in set (0.00 sec)
28.查询名字中含有「风」字的学生信息

mysql> select * from student where sname like '%风%';
+------+--------+---------------------+------+
| SId  | Sname  | Sage                | Ssex |
+------+--------+---------------------+------+
| 03   | 孙风   | 1990-12-20 00:00:00 | 男   |
+------+--------+---------------------+------+
1 row in set (0.00 sec)
29.查询同名同性学生名单，并统计同名人数

mysql> select sname,count(*) from student group by sname having count(*)>1;
+--------+----------+
| sname  | count(*) |
+--------+----------+
| 李四   |        2 |
+--------+----------+
1 row in set (0.00 sec)
30.查询 1990 年出生的学生名单

mysql> select * from student where year(sage)=1990;
+------+--------+---------------------+------+
| SId  | Sname  | Sage                | Ssex |
+------+--------+---------------------+------+
| 01   | 赵雷   | 1990-01-01 00:00:00 | 男   |
| 02   | 钱电   | 1990-12-21 00:00:00 | 男   |
| 03   | 孙风   | 1990-12-20 00:00:00 | 男   |
| 04   | 李云   | 1990-12-06 00:00:00 | 男   |
+------+--------+---------------------+------+
4 rows in set (0.01 sec)
31.查询每门课程的平均成绩，结果按平均成绩降序排列，平均成绩相同时，按课程编号升序排列

mysql> select cid,avg(score) averg from sc group by cid order by averg desc;
+------+----------+
| cid  | averg    |
+------+----------+
| 02   | 72.66667 |
| 03   | 68.50000 |
| 01   | 64.50000 |
+------+----------+
3 rows in set (0.00 sec)
32.查询平均成绩大于等于 85 的所有学生的学号、姓名和平均成绩

mysql> select st.sid,st.sname,b1.averg from student st inner join
    -> (select sid,avg(score) averg from sc group by sid having  averg>85) b1
    -> on(st.sid=b1.sid);
+------+--------+----------+
| sid  | sname  | averg    |
+------+--------+----------+
| 01   | 赵雷   | 89.66667 |
| 07   | 郑竹   | 93.50000 |
+------+--------+----------+
2 rows in set (0.00 sec)
33.查询课程名称为「数学」，且分数低于 60 的学生姓名和分数

mysql> select st.sname,b2.score
    -> from student st,
    -> (select sid,score from
    -> sc,(select cid from course where cname='数学') b1
    -> where sc.cid=b1.cid and score<60) b2
    -> where st.sid=b2.sid;
+--------+-------+
| sname  | score |
+--------+-------+
| 李云   |  30.0 |
+--------+-------+
1 row in set (0.00 sec)
34.查询所有学生的课程及分数情况（存在学生没成绩，没选课的情况）

mysql> select st.sname,cid,score from student st
    -> left join sc on st.sid=sc.sid;
+--------+------+-------+
| sname  | cid  | score |
+--------+------+-------+
| 赵雷   | 03   |  99.0 |
| 赵雷   | 02   |  90.0 |
| 赵雷   | 01   |  80.0 |
| 钱电   | 03   |  80.0 |
| 钱电   | 02   |  60.0 |
| 钱电   | 01   |  70.0 |
| 孙风   | 03   |  80.0 |
| 孙风   | 02   |  80.0 |
| 孙风   | 01   |  80.0 |
| 李云   | 03   |  20.0 |
| 李云   | 02   |  30.0 |
| 李云   | 01   |  50.0 |
| 周梅   | 02   |  87.0 |
| 周梅   | 01   |  76.0 |
| 吴兰   | 03   |  34.0 |
| 吴兰   | 01   |  31.0 |
| 郑竹   | 03   |  98.0 |
| 郑竹   | 02   |  89.0 |
| 张三   | NULL |  NULL |
| 李四   | NULL |  NULL |
| 李四   | NULL |  NULL |
| 赵六   | NULL |  NULL |
| 孙七   | NULL |  NULL |
+--------+------+-------+
23 rows in set (0.00 sec)

35.查询任何一门课程成绩在 70 分以上的姓名、课程名称和分数

mysql> select st.sname,c.cname,s.score from student st,course c,sc s
    -> where s.score>70
    -> and st.sid=s.sid
    -> and s.cid=c.cid;
+--------+--------+-------+
| sname  | cname  | score |
+--------+--------+-------+
| 赵雷   | 英语   |  99.0 |
| 赵雷   | 数学   |  90.0 |
| 赵雷   | 语文   |  80.0 |
| 钱电   | 英语   |  80.0 |
| 孙风   | 英语   |  80.0 |
| 孙风   | 数学   |  80.0 |
| 孙风   | 语文   |  80.0 |
| 周梅   | 数学   |  87.0 |
| 周梅   | 语文   |  76.0 |
| 郑竹   | 英语   |  98.0 |
| 郑竹   | 数学   |  89.0 |
+--------+--------+-------+
11 rows in set (0.00 sec)

36.查询不及格的课程

mysql> select cid from sc where score<60 group by cid;
+------+
| cid  |
+------+
| 01   |
| 02   |
| 03   |
+------+
3 rows in set (0.00 sec)
37.查询课程编号为 01 且课程成绩在 80 分以上的学生的学号和姓名

mysql> select distinct st.sid,st.sname from student st,sc
    -> where sc.cid=1 and sc.score>=80 and st.sid=sc.sid;
+------+--------+
| sid  | sname  |
+------+--------+
| 01   | 赵雷   |
| 03   | 孙风   |
+------+--------+
2 rows in set (0.00 sec)
38.求每门课程的学生人数

mysql> select cid,count(sid) from sc group by cid;
+------+------------+
| cid  | count(sid) |
+------+------------+
| 01   |          6 |
| 02   |          6 |
| 03   |          6 |
+------+------------+
3 rows in set (0.00 sec)
39.成绩不重复，查询选修「张三」老师所授课程的学生中，成绩最高的学生信息及其成绩

mysql> select student.*, sc.score, sc.cid from student, teacher, course,sc
    -> where teacher.tid = course.tid
    -> and sc.sid = student.sid
    -> and sc.cid = course.cid
    -> and teacher.tname = "张三"
    -> order by score desc
    -> limit 1;
+------+--------+---------------------+------+-------+------+
| SId  | Sname  | Sage                | Ssex | score | cid  |
+------+--------+---------------------+------+-------+------+
| 01   | 赵雷   | 1990-01-01 00:00:00 | 男   |  90.0 | 02   |
+------+--------+---------------------+------+-------+------+
1 row in set (0.00 sec)
41.查询不同课程成绩相同的学生的学生编号、课程编号、学生成绩

mysql> select distinct  a.cid, a.sid,  a.score from sc as a
    -> inner join
    -> sc as b
    -> on a.sid = b.sid
    -> and a.cid != b.cid
    -> and a.score = b.score;
+------+------+-------+
| cid  | sid  | score |
+------+------+-------+
| 03   | 03   |  80.0 |
| 02   | 03   |  80.0 |
| 01   | 03   |  80.0 |
+------+------+-------+
3 rows in set (0.01 sec)
42.查询每门功成绩最好的前两名

43.统计每门课程的学生选修人数（超过 5 人的课程才统计）。

mysql> select cid,count(sid) from sc group by cid having count(sid)>5;
+------+------------+
| cid  | count(sid) |
+------+------------+
| 01   |          6 |
| 02   |          6 |
| 03   |          6 |
+------+------------+
3 rows in set (0.00 sec)
44.检索至少选修两门课程的学生学号

mysql> select sid,count(cid) s from sc group by sid having s>-2;
+------+---+
| sid  | s |
+------+---+
| 01   | 3 |
| 02   | 3 |
| 03   | 3 |
| 04   | 3 |
| 05   | 2 |
| 06   | 2 |
| 07   | 2 |
+------+---+
7 rows in set (0.00 sec)
45.查询选修了全部课程的学生信息

mysql> select st.* from student st,
    -> (select sid from sc group by sid having count(cid)=(select count(*) from course)) b1
    -> where st.sid=b1.sid;
+------+--------+---------------------+------+
| SId  | Sname  | Sage                | Ssex |
+------+--------+---------------------+------+
| 01   | 赵雷   | 1990-01-01 00:00:00 | 男   |
| 02   | 钱电   | 1990-12-21 00:00:00 | 男   |
| 03   | 孙风   | 1990-12-20 00:00:00 | 男   |
| 04   | 李云   | 1990-12-06 00:00:00 | 男   |
+------+--------+---------------------+------+
4 rows in set (0.00 sec)
46.查询各学生的年龄，只按年份来算

mysql> select sname,year(curdate())-year(sage) 年龄 from student;
+--------+--------+
| sname  | 年龄   |
+--------+--------+
| 赵雷   |     33 |
| 钱电   |     33 |
| 孙风   |     33 |
| 李云   |     33 |
| 周梅   |     32 |
| 吴兰   |     31 |
| 郑竹   |     34 |
| 张三   |      6 |
| 李四   |      6 |
| 李四   |     11 |
| 赵六   |     10 |
| 孙七   |      9 |
+--------+--------+
12 rows in set (0.01 sec)

47.按照出生日期来算，当前月日 < 出生年月的月日则，年龄减一

mysql> select student.SId as 学生编号,student.Sname  as  学生姓名,
    -> TIMESTAMPDIFF(YEAR,student.Sage,CURDATE()) as 学生年龄
    -> from student
    -> ;
+--------------+--------------+--------------+
| 学生编号     | 学生姓名     | 学生年龄     |
+--------------+--------------+--------------+
| 01           | 赵雷         |           33 |
| 02           | 钱电         |           32 |
| 03           | 孙风         |           32 |
| 04           | 李云         |           32 |
| 05           | 周梅         |           31 |
| 06           | 吴兰         |           31 |
| 07           | 郑竹         |           34 |
| 09           | 张三         |            5 |
| 10           | 李四         |            5 |
| 11           | 李四         |           11 |
| 12           | 赵六         |           10 |
| 13           | 孙七         |            9 |
+--------------+--------------+--------------+
12 rows in set (0.01 sec)

48.查询本周过生日的学生

mysql> select *
    -> from student
    -> where WEEKOFYEAR(student.Sage)=WEEKOFYEAR(CURDATE());
Empty set (0.00 sec)
49.查询下周过生日的学生

mysql> select *
    -> from student
    -> where WEEKOFYEAR(student.Sage)=WEEKOFYEAR(CURDATE())+1;
Empty set (0.00 sec)
50.查询本月过生日的学生

mysql> select *
    -> from student
    -> where MONTH(student.Sage)=MONTH(CURDATE());
Empty set (0.01 sec)
51查询下月过生日的学生

mysql> select *
    -> from student
    -> where MONTH(student.Sage)=MONTH(CURDATE())+1;
Empty set (0.00 sec)