数据库50个练习

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);

练习题目

查询" 01 "课程比" 02 "课程成绩高的学生的信息及课程分数

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select s.*, sc1.score as score1, sc2.score as score2
from student s
join sc sc1 on s.sid = sc1.sid and sc1.cid = '01'
join sc sc2 on s.sid = sc2.sid and sc2.cid = '02'
where sc1.score > sc2.score;

查询同时存在" 01 "课程和" 02 "课程的情况

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SELECT s.*
FROM Student s
JOIN SC sc1 ON s.SId = sc1.SId AND sc1.CId = '01'
JOIN SC sc2 ON s.SId = sc2.SId AND sc2.CId = '02';

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 )

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SELECT s.*
FROM Student s
JOIN SC sc2 ON s.SId = sc2.SId AND sc2.CId = '02'
WHERE NOT EXISTS (
    SELECT 1 FROM SC WHERE SId = s.SId AND CId = '01'
);

查询不存在" 01 "课程但存在" 02 "课程的情况

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SELECT s.*
FROM Student s
JOIN SC sc2 ON s.SId = sc2.SId AND sc2.CId = '02'
WHERE NOT EXISTS (
    SELECT 1 FROM SC WHERE SId = s.SId AND CId = '01'
);

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

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SELECT s.SId, s.Sname, AVG(sc.score) AS avg_score
FROM Student s
JOIN SC sc ON s.SId = sc.SId
GROUP BY s.SId, s.Sname
HAVING AVG(sc.score) >= 60;

查询在 SC 表存在成绩的学生信息

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SELECT DISTINCT s.*
FROM Student s
JOIN SC sc ON s.SId = sc.SId;

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 )

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SELECT s.SId, s.Sname, 
       COUNT(sc.CId) AS course_count,
       SUM(sc.score) AS total_score
FROM Student s
LEFT JOIN SC sc ON s.SId = sc.SId
GROUP BY s.SId, s.Sname;

查有成绩的学生信息

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SELECT DISTINCT s.*
FROM Student s
WHERE EXISTS (SELECT 1 FROM SC WHERE SId = s.SId);

查询「李」姓老师的数量

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SELECT COUNT(*) AS li_teachers
FROM Teacher
WHERE Tname LIKE '李%';

查询学过「张三」老师授课的同学的信息

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SELECT DISTINCT s.*
FROM Student s
JOIN SC sc ON s.SId = sc.SId
JOIN Course c ON sc.CId = c.CId
JOIN Teacher t ON c.TId = t.TId
WHERE t.Tname = '张三';

查询没有学全所有课程的同学的信息

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SELECT s.*
FROM Student s
WHERE s.SId NOT IN (
    SELECT SId 
    FROM SC 
    GROUP BY SId 
    HAVING COUNT(DISTINCT CId) = (SELECT COUNT(*) FROM Course)
);

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

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SELECT DISTINCT s.*
FROM Student s
JOIN SC sc ON s.SId = sc.SId
WHERE sc.CId IN (
    SELECT CId FROM SC WHERE SId = '01'
) AND s.SId != '01';

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

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SELECT s.*
FROM Student s
WHERE s.SId IN (
    SELECT SId FROM SC WHERE SId != '01'
    GROUP BY SId
    HAVING GROUP_CONCAT(CId ORDER BY CId) = (
        SELECT GROUP_CONCAT(CId ORDER BY CId) 
        FROM SC 
        WHERE SId = '01'
    )
);

查询没学过"张三"老师讲授的任一门课程的学生姓名

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SELECT s.*
FROM Student s
WHERE s.SId NOT IN (
    SELECT DISTINCT sc.SId
    FROM SC sc
    JOIN Course c ON sc.CId = c.CId
    JOIN Teacher t ON c.TId = t.TId
    WHERE t.Tname = '张三'
);

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

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SELECT s.SId, s.Sname, AVG(sc.score) AS avg_score
FROM Student s
JOIN SC sc ON s.SId = sc.SId
WHERE sc.score < 60
GROUP BY s.SId, s.Sname
HAVING COUNT(*) >= 2;

检索" 01 "课程分数小于 60，按分数降序排列的学生信息

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SELECT s.*, sc.score
FROM Student s
JOIN SC sc ON s.SId = sc.SId
WHERE sc.CId = '01' AND sc.score < 60
ORDER BY sc.score DESC;

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

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SELECT s.SId, s.Sname, sc.CId, sc.score, 
       (SELECT AVG(score) FROM SC WHERE SId = s.SId) AS avg_score
FROM Student s
LEFT JOIN SC sc ON s.SId = sc.SId
ORDER BY avg_score DESC;

查询各科成绩最高分、最低分和平均分：

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SELECT 
    c.CId, 
    c.Cname, 
    MAX(sc.score) AS max_score,
    MIN(sc.score) AS min_score,
    AVG(sc.score) AS avg_score,
    COUNT(sc.SId) AS student_count,
    CONCAT(ROUND(SUM(CASE WHEN sc.score >= 60 THEN 1 ELSE 0 END) / COUNT(*) * 100, 2), '%') AS pass_rate,
    CONCAT(ROUND(SUM(CASE WHEN sc.score >= 70 AND sc.score < 80 THEN 1 ELSE 0 END) / COUNT(*) * 100, 2), '%') AS medium_rate,
    CONCAT(ROUND(SUM(CASE WHEN sc.score >= 80 AND sc.score < 90 THEN 1 ELSE 0 END) / COUNT(*) * 100, 2), '%') AS good_rate,
    CONCAT(ROUND(SUM(CASE WHEN sc.score >= 90 THEN 1 ELSE 0 END) / COUNT(*) * 100, 2), '%') AS excellent_rate
FROM Course c
LEFT JOIN SC sc ON c.CId = sc.CId
GROUP BY c.CId, c.Cname
ORDER BY student_count DESC, c.CId ASC;

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
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```
SELECT 
    sc.CId, 
    sc.SId, 
    sc.score,
    RANK() OVER (PARTITION BY sc.CId ORDER BY sc.score DESC) AS rank
FROM SC sc
ORDER BY sc.CId, rank;
```

按各科成绩进行排序，并显示排名， Score 重复时保留名次空缺

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SELECT 
    sc.CId, 
    sc.SId, 
    sc.score,
    DENSE_RANK() OVER (PARTITION BY sc.CId ORDER BY sc.score DESC) AS rank
FROM SC sc
ORDER BY sc.CId, rank;

按各科成绩进行排序，并显示排名， Score 重复时合并名次

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SELECT 
    s.SId, 
    s.Sname, 
    SUM(sc.score) AS total_score,
    RANK() OVER (ORDER BY SUM(sc.score) DESC) AS rank
FROM Student s
JOIN SC sc ON s.SId = sc.SId
GROUP BY s.SId, s.Sname
ORDER BY rank;

查询学生的总成绩，并进行排名，总分重复时保留名次空缺

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SELECT 
    s.SId, 
    s.Sname, 
    SUM(sc.score) AS total_score,
    DENSE_RANK() OVER (ORDER BY SUM(sc.score) DESC) AS rank
FROM Student s
JOIN SC sc ON s.SId = sc.SId
GROUP BY s.SId, s.Sname
ORDER BY rank;

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

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SELECT 
    s.SId, 
    s.Sname, 
    SUM(sc.score) AS total_score,
    DENSE_RANK() OVER (ORDER BY SUM(sc.score) DESC) AS rank
FROM Student s
JOIN SC sc ON s.SId = sc.SId
GROUP BY s.SId, s.Sname
ORDER BY rank;

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

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SELECT 
    c.CId,
    c.Cname,
    SUM(CASE WHEN sc.score BETWEEN 85 AND 100 THEN 1 ELSE 0 END) AS '[85-100]',
    CONCAT(ROUND(SUM(CASE WHEN sc.score BETWEEN 85 AND 100 THEN 1 ELSE 0 END) / COUNT(*) * 100, 2), '%') AS '[85-100]%',
    SUM(CASE WHEN sc.score BETWEEN 70 AND 85 THEN 1 ELSE 0 END) AS '[70-85]',
    CONCAT(ROUND(SUM(CASE WHEN sc.score BETWEEN 70 AND 85 THEN 1 ELSE 0 END) / COUNT(*) * 100, 2), '%') AS '[70-85]%',
    SUM(CASE WHEN sc.score BETWEEN 60 AND 70 THEN 1 ELSE 0 END) AS '[60-70]',
    CONCAT(ROUND(SUM(CASE WHEN sc.score BETWEEN 60 AND 70 THEN 1 ELSE 0 END) / COUNT(*) * 100, 2), '%') AS '[60-70]%',
    SUM(CASE WHEN sc.score BETWEEN 0 AND 60 THEN 1 ELSE 0 END) AS '[0-60]',
    CONCAT(ROUND(SUM(CASE WHEN sc.score BETWEEN 0 AND 60 THEN 1 ELSE 0 END) / COUNT(*) * 100, 2), '%') AS '[0-60]%'
FROM Course c
LEFT JOIN SC sc ON c.CId = sc.CId
GROUP BY c.CId, c.Cname;

查询各科成绩前三名的记录

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SELECT *
FROM (
    SELECT 
        sc.CId, 
        sc.SId, 
        sc.score,
        RANK() OVER (PARTITION BY sc.CId ORDER BY sc.score DESC) AS rank
    FROM SC sc
) t
WHERE t.rank <= 3;

查询每门课程被选修的学生数

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SELECT c.CId, c.Cname, COUNT(DISTINCT sc.SId) AS student_count
FROM Course c
LEFT JOIN SC sc ON c.CId = sc.CId
GROUP BY c.CId, c.Cname;

查询出只选修两门课程的学生学号和姓名

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SELECT s.SId, s.Sname
FROM Student s
JOIN SC sc ON s.SId = sc.SId
GROUP BY s.SId, s.Sname
HAVING COUNT(*) = 2;

查询男生、女生人数

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SELECT Ssex, COUNT(*) AS count
FROM Student
GROUP BY Ssex;

查询名字中含有「风」字的学生信息
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```
SELECT *
FROM Student
WHERE Sname LIKE '%风%';
```

查询同名同性学生名单，并统计同名人数

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SELECT Sname, Ssex, COUNT(*) AS same_name_count
FROM Student
GROUP BY Sname, Ssex
HAVING COUNT(*) > 1;

查询 1990 年出生的学生名单
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```
SELECT *
FROM Student
WHERE YEAR(Sage) = 1990;
```

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

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SELECT c.CId, c.Cname, AVG(sc.score) AS avg_score
FROM Course c
LEFT JOIN SC sc ON c.CId = sc.CId
GROUP BY c.CId, c.Cname
ORDER BY avg_score DESC, c.CId ASC;

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

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SELECT s.SId, s.Sname, AVG(sc.score) AS avg_score
FROM Student s
JOIN SC sc ON s.SId = sc.SId
GROUP BY s.SId, s.Sname
HAVING AVG(sc.score) >= 85;

查询课程名称为「数学」，且分数低于 60 的学生姓名和分数

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SELECT s.Sname, sc.score
FROM Student s
JOIN SC sc ON s.SId = sc.SId
JOIN Course c ON sc.CId = c.CId
WHERE c.Cname = '数学' AND sc.score < 60;

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）

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SELECT s.SId, s.Sname, c.Cname, sc.score
FROM Student s
LEFT JOIN SC sc ON s.SId = sc.SId
LEFT JOIN Course c ON sc.CId = c.CId;

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

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SELECT DISTINCT s.Sname, c.Cname, sc.score
FROM Student s
JOIN SC sc ON s.SId = sc.SId
JOIN Course c ON sc.CId = c.CId
WHERE sc.score > 70;

查询不及格的课程

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SELECT s.Sname, c.Cname, sc.score
FROM Student s
JOIN SC sc ON s.SId = sc.SId
JOIN Course c ON sc.CId = c.CId
WHERE sc.score < 60;

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

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SELECT s.SId, s.Sname
FROM Student s
JOIN SC sc ON s.SId = sc.SId
WHERE sc.CId = '01' AND sc.score > 80;

求每门课程的学生人数

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SELECT c.CId, c.Cname, COUNT(sc.SId) AS student_count
FROM Course c
LEFT JOIN SC sc ON c.CId = sc.CId
GROUP BY c.CId, c.Cname;

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

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SELECT s.*, sc.score
FROM Student s
JOIN SC sc ON s.SId = sc.SId
JOIN Course c ON sc.CId = c.CId
JOIN Teacher t ON c.TId = t.TId
WHERE t.Tname = '张三'
ORDER BY sc.score DESC
LIMIT 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

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SELECT s.*, sc.score
FROM Student s
JOIN SC sc ON s.SId = sc.SId
JOIN Course c ON sc.CId = c.CId
JOIN Teacher t ON c.TId = t.TId
WHERE t.Tname = '张三' AND sc.score = (
    SELECT MAX(score) 
    FROM SC 
    JOIN Course ON SC.CId = Course.CId
    JOIN Teacher ON Course.TId = Teacher.TId
    WHERE Teacher.Tname = '张三'
);

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

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SELECT DISTINCT a.SId, a.CId, a.score
FROM SC a
JOIN SC b ON a.SId = b.SId AND a.CId != b.CId AND a.score = b.score;

查询每门功成绩最好的前两名

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SELECT *
FROM (
    SELECT 
        sc.CId, 
        sc.SId, 
        sc.score,
        RANK() OVER (PARTITION BY sc.CId ORDER BY sc.score DESC) AS rank
    FROM SC sc
) t
WHERE t.rank <= 2;

统计每门课程的学生选修人数（超过 5 人的课程才统计）。

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SELECT c.CId, c.Cname, COUNT(sc.SId) AS student_count
FROM Course c
JOIN SC sc ON c.CId = sc.CId
GROUP BY c.CId, c.Cname
HAVING COUNT(sc.SId) > 5;

检索至少选修两门课程的学生学号

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SELECT SId
FROM SC
GROUP BY SId
HAVING COUNT(DISTINCT CId) >= 2;

查询选修了全部课程的学生信息

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SELECT s.*
FROM Student s
WHERE NOT EXISTS (
    SELECT c.CId FROM Course c
    WHERE NOT EXISTS (
        SELECT 1 FROM SC WHERE SC.SId = s.SId AND SC.CId = c.CId
    )
);

查询各学生的年龄，只按年份来算

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SELECT SId, Sname, YEAR(CURRENT_DATE) - YEAR(Sage) AS age
FROM Student;

按照出生日期来算，当前月日 < 出生年月的月日则，年龄减一

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SELECT 
    SId, 
    Sname, 
    CASE 
        WHEN MONTH(CURRENT_DATE) < MONTH(Sage) OR 
             (MONTH(CURRENT_DATE) = MONTH(Sage) AND DAY(CURRENT_DATE) < DAY(Sage))
        THEN YEAR(CURRENT_DATE) - YEAR(Sage) - 1
        ELSE YEAR(CURRENT_DATE) - YEAR(Sage)
    END AS age
FROM Student;

查询本周过生日的学生

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SELECT *
FROM Student
WHERE WEEKOFYEAR(Sage) = WEEKOFYEAR(CURRENT_DATE);

查询下周过生日的学生

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SELECT *
FROM Student
WHERE WEEKOFYEAR(Sage) = WEEKOFYEAR(CURRENT_DATE) + 1;

查询本月过生日的学生

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SELECT *
FROM Student
WHERE MONTH(Sage) = MONTH(CURRENT_DATE);

查询下月过生日的学生

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SELECT *
FROM Student
WHERE MONTH(Sage) = MONTH(CURRENT_DATE) + 1;