MySql---03

于 2025-04-06 18:44:22 发布
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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);

mysql> CREATE TABLE Student (
    ->     SId VARCHAR(10),
    ->     Sname VARCHAR(10),
    ->     Sage DATETIME,
    ->     Ssex VARCHAR(10)
    -> );
Query OK, 0 rows affected (0.03 sec)

mysql> INSERT INTO Student VALUES
    -> ('01', '赵雷', '1990-01-01', '男'),
    -> ('02', '钱电', '1990-12-21', '男'),
    -> ('03', '孙风', '1990-12-20', '男'),
    -> ('04', '李云', '1990-12-06', '男'),
    -> ('05', '周梅', '1991-12-01', '女'),
    -> ('06', '吴兰', '1992-01-01', '女'),
    -> ('07', '郑竹', '1989-01-01', '女'),
    -> ('09', '张三', '2017-12-20', '女'),
    -> ('10', '李四', '2017-12-25', '女'),
    -> ('11', '李四', '2012-06-06', '女'),
    -> ('12', '赵六', '2013-06-13', '女'),
    -> ('13', '孙七', '2014-06-01', '女');
Query OK, 12 rows affected (0.01 sec)
Records: 12  Duplicates: 0  Warnings: 0

mysql> CREATE TABLE Course (
    ->     CId VARCHAR(10),
    ->     Cname NVARCHAR(10),
    ->     TId VARCHAR(10)
    -> );
Query OK, 0 rows affected, 1 warning (0.02 sec)

mysql> INSERT INTO Course VALUES
    -> ('01', '语文', '02'),
    -> ('02', '数学', '01'),
    -> ('03', '英语', '03');
Query OK, 3 rows affected (0.01 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> CREATE TABLE Teacher (
    ->     TId VARCHAR(10),
    ->     Tname VARCHAR(10)
    -> );
Query OK, 0 rows affected (0.02 sec)

mysql>
mysql> INSERT INTO Teacher VALUES
    -> ('01', '张三'),
    -> ('02', '李四'),
    -> ('03', '王五');
Query OK, 3 rows affected (0.01 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> CREATE TABLE SC (
    ->     SId VARCHAR(10),
    ->     CId VARCHAR(10),
    ->     score DECIMAL(18, 1)
    -> );
Query OK, 0 rows affected (0.02 sec)

mysql>
mysql> INSERT INTO SC VALUES
    -> ('01', '01', 80),
    -> ('01', '02', 90),
    -> ('01', '03', 99),
    -> ('02', '01', 70),
    -> ('02', '02', 60),
    -> ('02', '03', 80),
    -> ('03', '01', 80),
    -> ('03', '02', 80),
    -> ('03', '03', 80),
    -> ('04', '01', 50),
    -> ('04', '02', 30),
    -> ('04', '03', 20),
    -> ('05', '01', 76),
    -> ('05', '02', 87),
    -> ('06', '01', 31),
    -> ('06', '03', 34),
    -> ('07', '02', 89),
    -> ('07', '03', 98);
Query OK, 18 rows affected (0.01 sec)
Records: 18  Duplicates: 0  Warnings: 0

mysql> show tables;
+-------------------+
| Tables_in_works50 |
+-------------------+
| course            |
| sc                |
| student           |
| teacher           |
+-------------------+
4 rows in set (0.01 sec)

练习题目

  1. 查询" 01 "课程比" 02 "课程成绩高的学生的信息及课程分数
mysql> SELECT * FROM Student RIGHT JOIN (
    ->     SELECT t1.SId, class1, class2 FROM
    ->         (SELECT SId, score AS class1 FROM sc WHERE sc.CId = '01') AS t1,
    ->         (SELECT SId, score AS class2 FROM sc WHERE sc.CId = '02') AS t2
    ->     WHERE t1.SId = t2.SId AND t1.class1 > t2.class2
    -> ) r ON Student.SId = r.SId;
+------+--------+---------------------+------+------+--------+--------+
| SId  | Sname  | Sage                | Ssex | SId  | class1 | class2 |
+------+--------+---------------------+------+------+--------+--------+
| 02   | 钱电   | 1990-12-21 00:00:00 | 男   | 02   |   70.0 |   60.0 |
| 04   | 李云   | 1990-12-06 00:00:00 | 男   | 04   |   50.0 |   30.0 |
+------+--------+---------------------+------+------+--------+--------+
2 rows in set (0.00 sec)
    1. 查询同时存在" 01 "课程和" 02 "课程的情况
mysql> SELECT * FROM
    ->     (SELECT * FROM sc WHERE sc.CId = '01') AS t1,
    ->     (SELECT * FROM sc WHERE sc.CId = '02') AS t2
    -> WHERE t1.SId = t2.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 (0.00 sec)
    1. 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 sc.CId = '01') AS t1
    -> LEFT JOIN
    ->     (SELECT * FROM sc WHERE sc.CId = '02') AS t2
    -> ON t1.SId = t2.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)

    1. 查询不存在" 01 "课程但存在" 02 "课程的情况
mysql> SELECT * FROM sc
    -> WHERE sc.SId NOT IN (
    ->     SELECT SId FROM sc WHERE sc.CId = '01'
    -> ) AND sc.CId = '02';
+------+------+-------+
| SId  | CId  | score |
+------+------+-------+
| 07   | 02   |  89.0 |
+------+------+-------+
1 row in set (0.00 sec)
  1. 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 Student.SId, Student.Sname, r.ss FROM Student RIGHT JOIN (
    ->     SELECT SId, AVG(score) AS ss FROM sc
    ->     GROUP BY SId
    ->     HAVING AVG(score) >= 60
    -> ) r ON Student.SId = r.SId;
+------+--------+----------+
| SId  | Sname  | ss       |
+------+--------+----------+
| 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)
  1. 查询在 SC 表存在成绩的学生信息

mysql> SELECT DISTINCT Student.*
    -> FROM Student, sc
    -> WHERE Student.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)
  1. 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 s.SId, s.Sname, r.coursenumber, r.scoresum
    -> FROM (
    ->     (SELECT Student.SId, Student.Sname FROM Student) s
    ->     LEFT JOIN
    ->     (SELECT sc.SId, SUM(sc.score) AS scoresum, COUNT(sc.CId) AS coursenumber FROM sc GROUP BY sc.SId) r
    ->     ON s.SId = r.SId
    -> );
+------+--------+--------------+----------+
| SId  | Sname  | coursenumber | scoresum |
+------+--------+--------------+----------+
| 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)

4.1 查有成绩的学生信息

  1. 查询「李」姓老师的数量
mysql> SELECT COUNT(*)
    -> FROM Teacher
    -> WHERE Tname LIKE '李%';
+----------+
| COUNT(*) |
+----------+
|        1 |
+----------+
1 row in set (0.00 sec)

  1. 查询学过「张三」老师授课的同学的信息
mysql> SELECT Student.*
    -> FROM Student, Teacher, Course, sc
    -> WHERE
    ->     Student.SId = sc.SId
    ->     AND Course.CId = sc.CId
    ->     AND Course.TId = Teacher.TId
    ->     AND Teacher.Tname = '张三';
+------+--------+---------------------+------+
| 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)
  1. 查询没有学全所有课程的同学的信息

mysql> SELECT * FROM Student
    -> WHERE Student.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)
  1. 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
mysql> select * from student
    -> where student.sid in (
    ->     select sc.sid from sc
    ->     where sc.cid in(
    ->         select sc.cid from sc
    ->         where sc.sid = '01'
    ->     )
    -> );
+------+--------+---------------------+------+
| 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)

mysql>
  1. 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
  2. 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,course,teacher
    ->     where
    ->         sc.cid = course.cid
    ->         and course.tid = teacher.tid
    ->         and teacher.tname= "张三"
    -> );
+------+--------+---------------------+------+
| 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)

  1. 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 student.SId, student.Sname,b.avg
    -> from student RIGHT JOIN
    -> (select sid, AVG(score) as avg from sc
    ->     where sid in (
    ->               select sid from sc
    ->               where score<60
    ->               GROUP BY sid
    ->               HAVING count(score)>1)
    ->     GROUP BY sid) b on student.sid=b.sid;
+------+--------+----------+
| SId  | Sname  | avg      |
+------+--------+----------+
| 04   | 李云   | 33.33333 |
| 06   | 吴兰   | 32.50000 |
+------+--------+----------+
2 rows in set (0.00 sec)

  1. 检索" 01 "课程分数小于 60，按分数降序排列的学生信息
mysql> select student.*, sc.score from student, sc
    -> where student.sid = sc.sid
    -> and sc.score < 60
    -> and cid = "01"
    -> ORDER BY sc.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)
  1. 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 *  from sc
    -> left join (
    ->     select sid,avg(score) as avscore from sc
    ->     group by sid
    ->     )r
    -> on sc.sid = r.sid
    -> order by avscore desc;
+------+------+-------+------+----------+
| SId  | CId  | score | sid  | avscore  |
+------+------+-------+------+----------+
| 07   | 02   |  89.0 | 07   | 93.50000 |
| 07   | 03   |  98.0 | 07   | 93.50000 |
| 01   | 01   |  80.0 | 01   | 89.66667 |
| 01   | 02   |  90.0 | 01   | 89.66667 |
| 01   | 03   |  99.0 | 01   | 89.66667 |
| 05   | 01   |  76.0 | 05   | 81.50000 |
| 05   | 02   |  87.0 | 05   | 81.50000 |
| 03   | 01   |  80.0 | 03   | 80.00000 |
| 03   | 02   |  80.0 | 03   | 80.00000 |
| 03   | 03   |  80.0 | 03   | 80.00000 |
| 02   | 01   |  70.0 | 02   | 70.00000 |
| 02   | 02   |  60.0 | 02   | 70.00000 |
| 02   | 03   |  80.0 | 02   | 70.00000 |
| 04   | 01   |  50.0 | 04   | 33.33333 |
| 04   | 02   |  30.0 | 04   | 33.33333 |
| 04   | 03   |  20.0 | 04   | 33.33333 |
| 06   | 01   |  31.0 | 06   | 32.50000 |
| 06   | 03   |  34.0 | 06   | 32.50000 |
+------+------+-------+------+----------+
18 rows in set (0.00 sec)
  1. 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)as 最高分,
    -> min(sc.score)as 最低分,
    -> AVG(sc.score)as 平均分,
    -> count(*)as 选修人数,
    -> sum(case when sc.score>=60 then 1 else 0 end )/count(*)as 及格率,
    -> sum(case when sc.score>=70 and sc.score<80 then 1 else 0 end )/count(*)as 中等率,
    -> sum(case when sc.score>=80 and sc.score<90 then 1 else 0 end )/count(*)as 优良率,
    -> sum(case when sc.score>=90 then 1 else 0 end )/count(*)as 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    | 选修人数     | 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)

  1. 按各科成绩进行排序，并显示排名， Score 重复时保留名次空缺
  2. 15.1 按各科成绩进行排序，并显示排名， Score 重复时合并名次
  3. 查询学生的总成绩，并进行排名，总分重复时保留名次空缺

16.1 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

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

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<a.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 |
+------+------+-------+
10 rows in set (0.00 sec)
  1. 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)
  1. 查询出只选修两门课程的学生学号和姓名
mysql> select student.sid, student.sname from student
    -> where student.sid in
    -> (select sc.sid from sc
    -> group by sc.sid
    -> having count(sc.cid)=2
    -> );
+------+--------+
| sid  | sname  |
+------+--------+
| 05   | 周梅   |
| 06   | 吴兰   |
| 07   | 郑竹   |
+------+--------+
3 rows in set (0.00 sec)
  1. 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)

  1. 查询名字中含有「风」字的学生信息
mysql> select *
    -> from student
    -> where student.Sname like '%风%'
    -> ;
+------+--------+---------------------+------+
| SId  | Sname  | Sage                | Ssex |
+------+--------+---------------------+------+
| 03   | 孙风   | 1990-12-20 00:00:00 | 男   |
+------+--------+---------------------+------+
1 row in set (0.00 sec)
  1. 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)

  1. 查询 1990 年出生的学生名单
mysql> select *
    -> from student
    -> where YEAR(student.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 (0.00 sec)
  1. 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
  2. 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
  3. 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 student.sname, sc.score from student, sc, course
    -> where student.sid = sc.sid
    -> and course.cid = sc.cid
    -> and course.cname = "数学"
    -> and sc.score < 60;
+--------+-------+
| sname  | score |
+--------+-------+
| 李云   |  30.0 |
+--------+-------+
1 row in set (0.00 sec)
  1. 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 student.sname, cid, score from student
    -> left join sc
    -> on student.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)
  1. 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 student.sname, course.cname,sc.score from student,course,sc
    -> where sc.score>70
    -> and student.sid = sc.sid
    -> and sc.cid = course.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)
  1. 查询不及格的课程
mysql> select DISTINCT sc.CId
    -> from sc
    -> where sc.score <60;
+------+
| CId  |
+------+
| 01   |
| 02   |
| 03   |
+------+
3 rows in set (0.00 sec)
  1. 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 student.sid,student.sname
    -> from student,sc
    -> where cid="01"
    -> and score>=80
    -> and student.sid = sc.sid;
+------+--------+
| sid  | sname  |
+------+--------+
| 01   | 赵雷   |
| 03   | 孙风   |
+------+--------+
2 rows in set (0.00 sec)
  1. 求每门课程的学生人数
mysql> select sc.CId,count(*) as 学生人数
    -> from sc
    -> GROUP BY sc.CId;
+------+--------------+
| CId  | 学生人数     |
+------+--------------+
| 01   |            6 |
| 02   |            6 |
| 03   |            6 |
+------+--------------+
3 rows in set (0.00 sec)
  1. 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)
  1. 成绩有重复的情况下，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"
    -> and sc.score = (
    ->     select Max(sc.score)
    ->     from sc,student, teacher, course
    ->     where teacher.tid = course.tid
    ->     and sc.sid = student.sid
    ->     and sc.cid = course.cid
    ->     and teacher.tname = "张三"
    -> );
+------+--------+---------------------+------+-------+------+
| SId  | Sname  | Sage                | Ssex | score | cid  |
+------+--------+---------------------+------+-------+------+
| 01   | 赵雷   | 1990-01-01 00:00:00 | 男   |  90.0 | 02   |
| 07   | 郑竹   | 1989-01-01 00:00:00 | 女   |  90.0 | 02   |
+------+--------+---------------------+------+-------+------+
2 rows in set (0.00 sec)
  1. 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
  2. 查询每门功成绩最好的前两名

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 sc.cid, count(sid) as cc from sc
    -> group by cid
    -> having cc >5;
+------+----+
| cid  | cc |
+------+----+
| 01   |  6 |
| 02   |  6 |
| 03   |  6 |
+------+----+
3 rows in set (0.00 sec)

  1. 检索至少选修两门课程的学生学号
mysql> select sid, count(cid) as cc from sc
    -> group by sid
    -> having cc>=2;
+------+----+
| sid  | cc |
+------+----+
| 01   |  3 |
| 02   |  3 |
| 03   |  3 |
| 04   |  3 |
| 05   |  2 |
| 06   |  2 |
| 07   |  2 |
+------+----+
7 rows in set (0.00 sec)
  1. 查询选修了全部课程的学生信息

查询各学生的年龄，只按年份来算

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         |           35 |
| 02           | 钱电         |           34 |
| 03           | 孙风         |           34 |
| 04           | 李云         |           34 |
| 05           | 周梅         |           33 |
| 06           | 吴兰         |           33 |
| 07           | 郑竹         |           36 |
| 09           | 张三         |            7 |
| 10           | 李四         |            7 |
| 11           | 李四         |           12 |
| 12           | 赵六         |           11 |
| 13           | 孙七         |           10 |
+--------------+--------------+--------------+
12 rows in set (0.00 sec)
  1. 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         |           35 |
| 02           | 钱电         |           34 |
| 03           | 孙风         |           34 |
| 04           | 李云         |           34 |
| 05           | 周梅         |           33 |
| 06           | 吴兰         |           33 |
| 07           | 郑竹         |           36 |
| 09           | 张三         |            7 |
| 10           | 李四         |            7 |
| 11           | 李四         |           12 |
| 12           | 赵六         |           11 |
| 13           | 孙七         |           10 |
+--------------+--------------+--------------+
12 rows in set (0.00 sec)
  1. 查询本周过生日的学生
  2. 查询下周过生日的学生
  3. 查询本月过生日的学生
  4. 查询下月过生日的学生
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