MySQL经典50题(必做）
花了几天时间终于敲完这50个题，期间也参考了很多博客上写的代码，每个题可能有好几种写法。
我也只是从去年开始接触MySQL，我记得我当时安装软件就装了好久，刚入门可能存在一些困难，但是都要一步一步来。
所以我也只是小白一枚，每个题我写的解法可能不是最优的，可能考虑的角度不是最全的，欢迎大家在评论区指正，一起交流进步。
软件工具：MySQL5.5 & SQLyog
/*
创建表
–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
*/
ALTER DATABASE students CHARACTER SET utf8;
CREATE TABLE student
(SID VARCHAR(10),Sname VARCHAR(20),Sage DATETIME,Ssex VARCHAR(10));
插入数据
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’ , ‘1990-05-20’ , ‘男’);
INSERT INTO Student VALUES(‘04’ , ‘李云’ , ‘1990-08-06’ , ‘男’);
INSERT INTO Student VALUES(‘05’ , ‘周梅’ , ‘1991-12-01’ , ‘女’);
INSERT INTO Student VALUES(‘06’ , ‘吴兰’ , ‘1992-03-01’ , ‘女’);
INSERT INTO Student VALUES(‘07’ , ‘郑竹’ , ‘1989-07-01’ , ‘女’);
INSERT INTO Student VALUES(‘08’ , ‘王菊’ , ‘1990-01-20’ , ‘女’);
CREATE TABLE Course(CID VARCHAR(10),Cname VARCHAR(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’);
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’);
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 s.*,a.score AS score01,b.score AS score02
FROM student AS s
JOIN SC AS a ON s.SID=a.SID AND a.CID=“01”
LEFT JOIN SC AS b ON s.SID=b.SID AND b.CID=“02”
OR b.CID = NULL
WHERE a.score>b.score;
2、查询"01"课程比"02"课程成绩低的学生的信息及课程分数
SELECT s.*,a.score AS score01,b.score AS score02
FROM student AS s
JOIN SC AS a ON s.SID=a.SID AND a.CID=“01”
LEFT JOIN SC AS b ON s.SID=b.SID AND b.CID=“02”
OR b.CID = NULL
WHERE a.score<b.score;
3、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 s.SID,s.Sname,AVG(a.score) AS avg_score
FROM student AS s
JOIN SC AS a ON s.SID=a.SID
GROUP BY a.SID
HAVING avg_score >= 60;
4、查询平均成绩小于60分的同学的学生编号和学生姓名和平均成绩
SELECT s.SID,s.Sname,AVG(a.score) AS avg_score
FROM student AS s
JOIN SC AS a ON s.SID=a.SID
GROUP BY a.SID
HAVING avg_score < 60;
5、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
#【这里一定要用外连接，因为有的同学没有选课，不然用内连接筛选不出来】
SELECT s.SID,s.Sname,COUNT(a.CID) AS 选课总数,SUM(a.score) AS 总成绩
FROM student AS s
LEFT JOIN SC AS a ON s.SID=a.SID
GROUP BY a.SID,s.Sname;
#6、查询"李"姓老师的数量
SELECT COUNT(*)
FROM teacher
WHERE Tname LIKE ‘李%’;
#7、查询学过"张三"老师授课的同学的信息
#方法一：
SELECT s.*
FROM student AS s
JOIN SC AS a ON s.SID=a.SID
JOIN course AS c ON c.CID=a.CID
JOIN teacher AS t ON t.TID=c.TID
WHERE t.Tname = ‘张三’;
方法二：
SELECT s.*
FROM student AS s
JOIN SC AS a ON s.SID=a.SID
WHERE a.CID IN(
SELECT CID FROM course AS c
WHERE TID=(
SELECT TID FROM teacher AS t
WHERE t.Tname=‘张三’)
);
–8、查询没学过"张三"老师授课的同学的信息
SELECT s.*
FROM student AS s
WHERE s.SID NOT IN (
SELECT a.SID FROM student AS a JOIN SC AS b ON a.SID=b.SID
WHERE b.CID IN (
SELECT c.CID FROM course AS c JOIN teacher AS t ON c.TID=t.TID
WHERE t.Tname=‘张三’)
);
#–9、查询学过编号为"01"并且也学过编号为"02"的课程的同学的信息
SELECT s.*,a.CID,b.CID
FROM student AS s,SC AS a,SC AS b
WHERE s.SID=a.SID
AND s.SID=b.SID
AND a.CID=‘01’
AND b.CID=‘02’;
#–10、查询学过编号为"01"但是没有学过编号为"02"的课程的同学的信息
SELECT s.*
FROM student AS s
WHERE s.SID IN (
SELECT SID FROM SC WHERE CID=‘01’
)
AND s.SID NOT IN(
SELECT SID FROM SC WHERE CID=‘02’
);
#–11、查询没有学全所有课程的同学的信息
SELECT s.*
FROM student AS s
LEFT JOIN SC AS a ON s.SID=a.SID
GROUP BY s.SID
HAVING COUNT(s.SID)< (SELECT COUNT(*) FROM course);
–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
#方法一：
SELECT DISTINCT s.*
FROM student AS s
JOIN SC AS a ON s.SID=a.SID
WHERE a.CID IN (
SELECT CID
FROM student AS s
JOIN SC AS a ON s.SID=a.SID
WHERE s.SID=‘01’
);
#方法二：
SELECT * FROM student
WHERE SID IN(
SELECT DISTINCT a.SID FROM SC a
WHERE a.CID IN(SELECT a.CID FROM SC a WHERE a.SID=‘01’)
);
–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
SELECT s.*
FROM student AS s
JOIN SC AS a ON s.SID=a.SID
GROUP BY a.SID
HAVING GROUP_CONCAT(a.CID) = (
SELECT GROUP_CONCAT(CID)
FROM SC
GROUP BY SID
HAVING SID = ‘01’)
AND a.SID != ‘01’;
#–14、查询没学过"张三"老师讲授的任一门课程的学生姓名
SELECT s.Sname
FROM student AS s
WHERE s.SID NOT IN (
SELECT SID FROM SC AS a
WHERE CID = (
SELECT CID FROM course AS c
JOIN teacher AS t ON c.TID=t.TID
WHERE t.Tname=‘张三’)
);
#–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
SELECT s.SID,s.Sname,AVG(a.score) AS 平均成绩
FROM student AS s
LEFT JOIN SC AS a ON s.SID=a.SID
WHERE s.SID IN (
SELECT SID FROM SC WHERE score<60
GROUP BY SID
HAVING COUNT(*)>=2
)
GROUP BY s.SID,s.Sname;
#–16、检索"01"课程分数小于60，按分数降序排列的学生信息
方法一：
SELECT s.*,a.score
FROM student AS s,SC AS a
WHERE s.SID=a.SID
AND a.CID=‘01’
AND a.score<60
ORDER BY score DESC;
方法二：
SELECT s.*,a.score
FROM student AS s
LEFT JOIN SC AS a ON s.SID=a.SID
WHERE a.CID=‘01’
AND a.score<60
ORDER BY score DESC;
–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
这个题做得我头挺大的 最后参考了别人写的代码
SELECT s.SID,s.Sname,
SUM(CASE WHEN a.CID='01’THEN IFNULL(a.score,0)ELSE 0 END) AS ‘语文’,
SUM(CASE WHEN a.CID='02’THEN IFNULL(a.score,0)ELSE 0 END) AS ‘数学’,
SUM(CASE WHEN a.CID='02’THEN IFNULL(a.score,0)ELSE 0 END) AS ‘英语’,
ROUND(AVG(a.score),2) AS 平均成绩
FROM SC AS a
LEFT JOIN student AS s ON a.SID=s.SID
GROUP BY a.SID
UNION
SELECT s1.SID,s1.Sname,0 AS ‘语文’,0 AS ‘数学’,0 AS ‘英语’,0 AS ‘平均成绩’
FROM student AS s1
WHERE s1.SID NOT IN (SELECT DISTINCT SID FROM SC)
ORDER BY 平均成绩 DESC;
#–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
SELECT a.CID,b.Cname,MAX(a.score) AS 最高分,MIN(a.score) AS 最低分,AVG(a.score) AS 平均分,
ROUND(100*(SUM(CASE WHEN a.score>=60 THEN 1 ELSE 0 END)/SUM(CASE WHEN a.score THEN 1 ELSE 0 END)),2) AS 及格率,
ROUND(100*(SUM(CASE WHEN a.score>=70 AND a.score<80 THEN 1 ELSE 0 END)/SUM(CASE WHEN a.score THEN 1 ELSE 0 END)),2) AS 中等率,
ROUND(100*(SUM(CASE WHEN a.score>=80 AND a.score<90 THEN 1 ELSE 0 END)/SUM(CASE WHEN a.score THEN 1 ELSE 0 END)),2) AS 优良率,
ROUND(100*(SUM(CASE WHEN a.score>=90 THEN 1 ELSE 0 END)/SUM(CASE WHEN a.score THEN 1 ELSE 0 END)),2) AS 优秀率
FROM SC AS a
LEFT JOIN course AS b ON a.CID=b.CID
GROUP BY a.CID,b.Cname;
–19、按各科成绩进行排序，并显示排名
#(我觉得这个题使用开窗函数蛮好的，但我用的mysql5.5不支持开窗函数，我就不用这个方法了)
SELECT a.* , (SELECT COUNT(DISTINCT score) FROM SC WHERE CID = a.CID AND score >a.score) +1
AS 排名 FROM SC AS a ORDER BY a.cid , 排名;
–20、查询学生的总成绩并进行排名（没做完）
SELECT s.SID,s.Sname,SUM(a.score) AS 总成绩
FROM student AS s
LEFT JOIN SC AS a ON s.SID=a.SID
GROUP BY s.SID,s.Sname
ORDER BY 总成绩;
–21、查询不同老师所教不同课程平均分从高到低显示
SELECT t.TID,t.Tname,ROUND(AVG(a.score),2) AS 平均分,c.CID
FROM course AS c
LEFT JOIN teacher AS t ON t.TID=c.TID
LEFT JOIN SC AS a ON a.CID=c.CID
GROUP BY t.TID
ORDER BY 平均分 DESC;
–22、查询所有课程的成绩第2名到第3名的学生信息及该课程成绩
SELECT a.* , (SELECT COUNT(DISTINCT score) FROM SC WHERE CID = a.CID AND score > a.score) + 1 AS 排名
FROM SC AS a HAVING 排名 BETWEEN 2 AND 3 ORDER BY a.CID,排名;
–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 , 0-60 及所占百分比
SELECT DISTINCT f.Cname,a.CID,b.85-100,b.百分比,c.70-85,c.百分比,d.60-70,d.百分比,e.0-60,e.百分比 FROM SC AS a
LEFT JOIN (SELECT CID,SUM(CASE WHEN score >85 AND score <=100 THEN 1 ELSE 0 END) AS 85-100,
ROUND(100*(SUM(CASE WHEN score >85 AND score <=100 THEN 1 ELSE 0 END)/COUNT()),2) AS 百分比
FROM SC GROUP BY CID) AS b ON a.CID=b.CID
LEFT JOIN (SELECT CID,SUM(CASE WHEN score >70 AND score <=85 THEN 1 ELSE 0 END) AS 70-85,
ROUND(100(SUM(CASE WHEN score >70 AND score <=85 THEN 1 ELSE 0 END)/COUNT()),2) AS 百分比
FROM SC GROUP BY CID) AS c ON a.CID=c.CID
LEFT JOIN (SELECT CID,SUM(CASE WHEN score >60 AND score <=70 THEN 1 ELSE 0 END) AS 60-70,
ROUND(100(SUM(CASE WHEN score >60 AND score <=70 THEN 1 ELSE 0 END)/COUNT()),2) AS 百分比
FROM SC GROUP BY CID) AS d ON a.CID=d.CID
LEFT JOIN (SELECT CID,SUM(CASE WHEN score >=0 AND score <=60 THEN 1 ELSE 0 END) AS 0-60,
ROUND(100(SUM(CASE WHEN score >=0 AND score <=60 THEN 1 ELSE 0 END)/COUNT(*)),2) AS 百分比
FROM SC GROUP BY CID)e ON a.CID=e.CID
LEFT JOIN course AS f ON a.CID = f.CID;
–24、查询学生平均成绩及其名次
SELECT t1.*,(SELECT COUNT(1) FROM (
SELECT s.SID,s.Sname,AVG(a.score) AS 平均成绩
FROM student AS s
LEFT JOIN SC AS a ON s.SID = a.SID
GROUP BY s.SID,s.Sname) AS t2
WHERE 平均成绩>t1.平均成绩)+1 AS 排名
FROM
( SELECT s.SID,s.Sname,AVG(a.score) AS 平均成绩
FROM student AS s
LEFT JOIN SC AS a ON s.SID = a.SID
GROUP BY s.SID,s.Sname) AS t1
ORDER BY 排名;
–25、查询各科成绩前三名的记录
SELECT a.SID,a.CID,a.score,COUNT(b.score) +1 AS 排名
FROM SC AS a
LEFT JOIN SC AS b ON a.CID=b.CID AND a.score<b.score
GROUP BY a.SID,a.CID,a.score
HAVING COUNT(b.SID)❤️
ORDER BY a.CID,排名 ;
–26、查询每门课程被选修的学生数
SELECT a.CID,COUNT(a.SID)
FROM SC AS a
GROUP BY a.CID;
–27、查询出只有两门课程的全部学生的学号和姓名
SELECT s.SID,s.Sname
FROM student AS s
JOIN SC AS a ON s.SID=a.SID
GROUP BY s.SID,s.Sname
HAVING COUNT(a.CID)=2;
#–28、查询男生、女生人数
SELECT s.Ssex,COUNT(s.Ssex) AS 人数
FROM student AS s
GROUP BY s.Ssex;
–29、查询名字中含有"风"字的学生信息
SELECT s.*
FROM student AS s
WHERE s.Sname LIKE ‘%风%’;
#–30、查询同名同性学生名单，并统计同名人数
SELECT a.Sname,a.Ssex
FROM student AS a
JOIN student AS b ON a.SID=b.SID AND a.Sname=b.Sname AND a.Ssex=b.Ssex
GROUP BY a.SID,a.Sname
HAVING COUNT(*)>1;
–31、查询1990年出生的学生名单(注：Student表中Sage列的类型是datetime)
SELECT s.*
FROM student AS s
WHERE s.Sage LIKE ‘1990%’;
–32、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 a.CID,ROUND(AVG(a.score),2) AS 平均成绩
FROM SC AS a
GROUP BY a.CID
ORDER BY 平均成绩 DESC,a.CID ASC;
–33、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 s.SID,s.Sname,ROUND(AVG(a.score),2) AS 平均成绩
FROM student AS s
LEFT JOIN SC AS a ON s.SID=a.SID
GROUP BY s.SID,s.Sname
HAVING 平均成绩 >= 85;
-34、查询课程名称为"数学"，且分数低于60的学生姓名和分数
SELECT s.Sname,a.score
FROM SC AS a
LEFT JOIN student AS s ON a.SID=s.SID
LEFT JOIN course AS c ON a.CID=c.CID
WHERE c.Cname=‘数学’
AND a.score<60;
–35、查询所有学生的课程及分数情况；
SELECT s.*,a.CID,c.Cname,a.score
FROM student AS s,SC AS a,course AS c
WHERE s.SID=a.SID AND a.CID=c.CID
GROUP BY s.SID,a.CID
ORDER BY s.SID,a.CID;
–36、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 s.Sname,a.score,c.Cname
FROM SC AS a
LEFT JOIN student AS s ON a.SID=s.SID
LEFT JOIN course AS c ON a.CID=c.CID
WHERE a.score>70
GROUP BY s.SID,a.CID;
–37、查询不及格的课程
SELECT s.*,a.CID,c.Cname,a.score
FROM SC AS a
JOIN course AS c ON a.CID=c.CID
JOIN student AS s ON a.SID=s.SID
WHERE a.score<60;
-38、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 s.SID,s.Sname,a.CID,a.score
FROM student AS s
LEFT JOIN SC AS a ON s.SID=a.SID
WHERE a.CID=01
AND a.score>=80;
-39、求每门课程的学生人数
SELECT a.CID,COUNT(a.CID)AS 学生人数
FROM SC AS a
GROUP BY a.CID;
–40、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
SELECT s.*,a.CID,a.score,t.Tname
FROM student AS s
JOIN SC AS a ON a.SID=s.SID
JOIN course AS c ON c.CID=a.CID
JOIN teacher AS t ON t.TID=c.TID
WHERE t.Tname=‘张三’
AND a.score IN (
SELECT MAX(score) FROM SC AS a
JOIN course AS c ON c.CID=a.CID
JOIN teacher AS t ON t.TID=c.TID
WHERE t.Tname=‘张三’
);
#–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
SELECT a.*
FROM SC AS a,(
SELECT CID,score
FROM SC
GROUP BY CID ,score
HAVING COUNT(1)>1
) AS b
WHERE a.CID=b.CID
AND a.score=b.score
ORDER BY a.CID,a.SID,a.score;
#–42、查询每门功课成绩最好的前两名
SELECT a.CID,a.SID,a.score
FROM SC AS a
WHERE (
SELECT COUNT(1) FROM SC AS b
WHERE b.CID=a.CID
AND b.score>=a.score
) <= 2
ORDER BY a.CID;
–43、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 a.CID,COUNT() AS 选修人数
FROM SC AS a
GROUP BY a.CID
HAVING COUNT()>5
ORDER BY 选修人数 DESC,a.CID ASC;
–44、检索至少选修两门课程的学生学号
SELECT a.SID,COUNT() AS 选修课程数
FROM SC AS a
GROUP BY a.SID
HAVING COUNT()>=2;
–45、查询选修了全部课程的学生信息
SELECT s.,COUNT() AS 选修课程数
FROM student AS s,SC AS a
WHERE s.SID=a.SID
GROUP BY a.SID
HAVING COUNT(*)>=3;
SELECT *
FROM student
WHERE SID IN (
SELECT SID FROM SC
GROUP BY SID
HAVING COUNT()=(SELECT COUNT() FROM course)
);
–46、查询各学生的年龄
#1.只按年份来算
SELECT SID,Sname,YEAR(NOW())-YEAR(Sage) AS 年龄
FROM student AS s；
#2.按出生日期来算，过了生日那一天肯定就是大一岁了
SELECT SID,Sname,Sage,(DATE_FORMAT(NOW(),’%Y’)-DATE_FORMAT(Sage,’%Y’)-
(CASE
WHEN DATE_FORMAT(NOW(),’%m%d’)>DATE_FORMAT(Sage,’%m%d’)
THEN 0
ELSE 1
END)) AS 年龄
FROM student;
–47、查询本周过生日的学生
SELECT *
FROM student
WHERE WEEK(DATE_FORMAT(NOW(),’%Y%m%d’))=WEEK(Sage);
–48、查询下周过生日的学生
SELECT *
FROM student
WHERE WEEK(DATE_FORMAT(NOW(),’%Y%m%d’))+1=WEEK(Sage);
–49、查询本月过生日的学生
SELECT *
FROM student
WHERE MONTH(DATE_FORMAT(NOW(),’%Y%m%d’))=MONTH(Sage);
-50、查询下月过生日的学生
SELECT *
FROM student
WHERE MONTH(DATE_FORMAT(NOW(),’%Y%m%d’))+1=MONTH(Sage);
过段时间再来刷一遍…