sql 练习

-- 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
    *
FROM
    (
        SELECT
            *
        FROM
            sc
        WHERE
            sc.Cno = ‘01‘
    ) sc1
JOIN (
    SELECT
        *
    FROM
        sc
    WHERE
        sc.Cno = ‘02‘
) sc2 ON sc1.sno = sc2.sno
WHERE
    sc1.score > sc2.score;

--  1.1 查询同时存在" 01 "课程和" 02 "课程的情况
SELECT
    *
FROM
    (
        SELECT
            *
        FROM
            sc
        WHERE
            sc.Cno = ‘01‘
    ) sc1
LEFT JOIN (
    SELECT
        *
    FROM
        sc
    WHERE
        sc.Cno = ‘02‘
) sc2 ON sc1.sno = sc2.sno
WHERE
    sc2.sno IS NOT NULL;

-- 1.2 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 )
SELECT
    *
FROM
    (
        SELECT
            *
        FROM
            sc
        WHERE
            sc.Cno = ‘01‘
    ) sc1
LEFT JOIN (
    SELECT
        *
    FROM
        sc
    WHERE
        sc.Cno = ‘02‘
) sc2 ON sc1.sno = sc2.sno;

-- 查询不存在" 01 "课程但存在" 02 "课程的情况
SELECT
    *
FROM
    sc
WHERE
    sc.Cno = ‘02‘
AND sc.Sno NOT IN (
    SELECT
        sc.sno
    FROM
        sc
    WHERE
        sc.Cno = ‘01‘
);

-- 2. 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  
SELECT
    st.sno,
    st.Sname,
    sc2.score
FROM
    student st
JOIN (
    SELECT
        sc.sno,
        AVG(sc.score) AS score
    FROM
        sc
    GROUP BY
        sc.sno
    HAVING
        AVG(sc.score) >= 60
) sc2 ON sc2.sno = st.Sno;

-- 3. 查询在 SC 表存在成绩的学生信息 
SELECT
    *
FROM
    student
WHERE
    student.Sno IN (SELECT sno FROM sc GROUP BY sno);

SELECT
    *
FROM
    student
WHERE
    student.Sno IN (SELECT DISTINCT sno FROM sc);

SELECT
    st.*
FROM
    student st
WHERE
    EXISTS (
        SELECT
            *
        FROM
            sc s
        WHERE
            s.sno = st.sno
    );

-- 4. 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)  
SELECT
    A.Sno AS 学生编号,
    A.Sname AS 学生姓名,
    B.`选课数量`,
    B.`总成绩`
FROM
    student AS A
LEFT JOIN (
    SELECT
        sc.Sno,
        COUNT(sc.score) AS 选课数量,
        SUM(sc.score) AS 总成绩
    FROM
        sc
    GROUP BY
        sc.Sno
) AS B ON A.Sno = B.Sno;

-- 4.1 查有成绩的学生信息
SELECT
    *
FROM
    student S
JOIN (
    SELECT
        sc.Sno
    FROM
        sc
    GROUP BY
        sc.Sno
) A ON S.Sno = A.Sno;

SELECT
    *
FROM
    student s
WHERE
    EXISTS (
        SELECT
            *
        FROM
            (
                SELECT
                    sc.Sno
                FROM
                    sc
                GROUP BY
                    sc.Sno
            ) A
        WHERE
            s.sno = A.sno
    );

-- 5.查询「李」姓老师的数量   
SELECT
    count(*)
FROM
    teacher
WHERE
    Tname LIKE ‘李%‘;

-- 6.查询学过「张三」老师授课的同学的信息
SELECT
    *
FROM
    student
WHERE
    student.Sno IN (
        SELECT
            Sno
        FROM
            sc
        WHERE
            sc.Cno IN (
                SELECT
                    Cno
                FROM
                    course
                WHERE
                    course.Tno IN (
                        SELECT
                            Tno
                        FROM
                            teacher
                        WHERE
                            Tname = ‘张三‘
                    )
            )
    ) -- 7.查询没有学全所有课程的同学的信息
    SELECT
        student.*
    FROM
        student
    LEFT JOIN (SELECT sno FROM sc GROUP BY sno) s1 ON s1.sno = student.Sno
    WHERE
        s1.sno IS NULL -- 查出没学的
    UNION
        SELECT
            student.*
        FROM
            student
        JOIN (
            SELECT
                sno
            FROM
                sc
            GROUP BY
                sno
            HAVING
                COUNT(1) < (SELECT COUNT(1) FROM course)
        ) s2 ON s2.sno = student.Sno;

-- 查出没学全的
-- 8. 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
SELECT
    *
FROM
    student
WHERE
    student.Sno IN (
        SELECT DISTINCT
            sc.Sno
        FROM
            sc
        WHERE
            sc.Cno IN (
                SELECT
                    cno
                FROM
                    sc
                WHERE
                    sc.Sno = ‘01‘
            )
    );

-- 9. 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
SELECT
    *
FROM
    Student
WHERE
    Sno IN (
        SELECT
            Sno
        FROM
            SC
        WHERE
            Cno IN (
                SELECT DISTINCT
                    Cno
                FROM
                    SC
                WHERE
                    Sno = ‘01‘
            )
        AND Sno <> ‘01‘
        GROUP BY
            Sno
        HAVING
            COUNT(Cno) >= 3
    );

-- 10. 查询没学过「张三」老师讲授的任一门课程的学生姓名 
SELECT
    *
FROM
    student
WHERE
    student.Sno NOT IN (
        SELECT
            sno
        FROM
            sc
        WHERE
            sc.Cno IN (
                SELECT
                    course.cno
                FROM
                    course
                WHERE
                    course.Tno = (
                        SELECT
                            tno
                        FROM
                            teacher
                        WHERE
                            teacher.Tname = ‘张三‘
                    )
            )
    );

-- 11.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
SELECT
    student.*, s2.avg
FROM
    student
JOIN (
    SELECT
        sc.Sno,
        AVG(sc.score) AS avg
    FROM
        sc
    WHERE
        sc.score < 60
    GROUP BY
        sc.Sno
    HAVING
        COUNT(1) >= 2
) s2 ON s2.Sno = student.Sno -- 12.检索" 01 "课程分数小于 60 ，按分数降序排列的学生信息   
SELECT
    *
FROM
    sc
WHERE
    sc.Cno = ‘01‘
AND sc.score < 60
ORDER BY
    sc.score DESC;

-- 13. （静态写法）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
SELECT
    info.sno AS 学号,
    info.Sname AS 学生姓名,
    SUM(
        CASE info.Cname
        WHEN ‘语文‘ THEN
            info.score
        END
    ) AS 语文,
    SUM(
        CASE info.Cname
        WHEN ‘数学‘ THEN
            info.score
        END
    ) AS 数学,
    SUM(
        CASE info.Cname
        WHEN ‘英语‘ THEN
            info.score
        END
    ) AS 英语,
    SUM(info.score)/3 AS 平均分
FROM
    (
        SELECT
            student.sno,
            student.Sname,
            course.Cname,
            sc.score
        FROM
            sc
        JOIN student ON sc.Sno = student.Sno
        JOIN course ON sc.Cno = course.Cno
    ) AS info
GROUP BY
    info.sno


-- 19. 查询每门课程被选修的学生数  

select  sc.Cno ,count(1) from  sc group by  sc.Cno ;


-- 20. 查询出只选修两门课程的学生学号和姓名   


SELECT
    *
FROM
    student
WHERE
    EXISTS (
        SELECT
            *
        FROM
            (
                SELECT
                    sc.Sno
                FROM
                    sc
                GROUP BY
                    sc.Sno
                HAVING
                    COUNT(1) = 2
            ) a
        WHERE
            a.Sno = student.Sno
    );



SELECT
    *
FROM
    student
WHERE
    student.Sno IN (
        SELECT
            sc.Sno
        FROM
            sc
        GROUP BY
            sc.Sno
        HAVING
            COUNT(1) = 2
    );

-- 21. 查询男生、女生人数  
  
select Ssex,COUNT(Ssex)人数 from Student group by Ssex    ;

-- 22. 查询名字中含有「风」字的学生信息 
select  * from  student where student.Sname like  ‘%风%‘;

-- 23. 查询同名同性学生名单，并统计同名人数 

SELECT
    Sname,
    Ssex,
    COUNT(*) 同名人数
FROM
    Student
GROUP BY
    Sname,
    Ssex
HAVING
    COUNT(*) > 1;

-- 24.查询 1990 年出生的学生名单 
select  * from  student where year(student.Sage)=‘1990‘;

-- 25. 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  

select  sc.Cno,AVG(sc.score) as score from  sc  GROUP BY sc.Cno ORDER BY score desc ,cno asc;


-- 26. 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

select  student.sno,student.Sname,a.scoreavg from  student  join(
select  sc.Sno,AVG(sc.score) as scoreavg  from  sc group  by  sc.Sno HAVING AVG(sc.score)>=85
)a on  a.Sno=student.Sno;


-- 27. 查询课程名称为「数学」，且分数低于 60 的学生姓名和分数
SELECT
    student.Sno,
    student.Sname,
    course.Cname,
    sc.score
FROM
    sc
LEFT JOIN student ON student.Sno = sc.sno
LEFT JOIN course  ON course.Cno=sc.Cno
WHERE
    sc.score < 60
AND EXISTS (
    SELECT
        *
    FROM
        (
            SELECT
                *
            FROM
                course
            WHERE
                course.Cname = ‘数学‘
        ) a
    WHERE
        a.cno = sc.Cno
);


-- 28. 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）


SELECT
    student.sno,
    student.Sname,
    course.Cname,
    sc.score
FROM
    student
LEFT JOIN sc ON sc.Sno = student.Sno
LEFT JOIN course ON course.Cno = sc.Cno;


-- 29. 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
select  * from  sc where EXISTS (select  * from  (select  sno from  sc  where  sc.score>=80 GROUP BY sc.Sno HAVING COUNT(1)>=(select  count(1) from  course)) a where a.sno= sc.sno );


-- 30. 查询不及格的课程
select course.Cname  from  sc   join course  on  course.Cno=sc.Cno   where sc.score<60 GROUP BY course.Cname;


-- 31. 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


SELECT
    student.Sno,
    student.Sname,
    a.score
FROM
    student
JOIN (
    SELECT
        *
    FROM
        sc
    WHERE
        sc.Cno = ‘01‘
    AND sc.score >= 80
) a ON a.sno = student.sno


-- 32. 求每门课程的学生人数   
select  sc.cno as 课程编号 ,COUNT(1)  as 人数 from  sc   GROUP BY sc.Cno

--  33.选修张三老师的课程的学生中,成绩最高
SELECT
    student.Sname, sc.score
FROM
    sc
JOIN student ON student.sno = sc.Sno
WHERE
    sc.score = (
        SELECT
            MAX(sc.score)
        FROM
            sc
        WHERE
            sc.Cno IN (
                SELECT
                    cno
                FROM
                    course
                WHERE
                    course.Tno = (
                        SELECT
                            tno
                        FROM
                            teacher
                        WHERE
                            teacher.Tname = ‘张三‘
                    )
            )
    );


-- 37.统计每门课程的学生选修人数（超过5人的课程才统计）。  
-- 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 
select  sc.cno,COUNT(1) as num from  sc group  by  sc.Cno  HAVING COUNT(1)>5 order  by  num desc ,sc.cno ;

-- 38. 检索至少选修两门课程的学生学号 
select sc.Sno,COUNT(1) from  sc group  by  sc.Sno HAVING COUNT(1)>2;


-- 39. 查询选修了全部课程的学生信息
select  sc.Sno,COUNT(1) from  sc  group  by  sc.Sno HAVING COUNT(1)=(select  COUNT(1) from  course);


-- 40. 查询各学生的年龄，只按年份来算 
select  student.sno,student.Sname,(YEAR(SYSDATE())-YEAR(student.Sage)) as age from  student