练习数据库下载地址https://files.cnblogs.com/files/xyhome/hellodb.rar
一 、导入hellodb.sql生成数据库后实现以下操作
# mysql -u username -p password < hellodb.sql
mysql> SHOW DATABASES; 可以列出已存在的数据库
+--------------------+
| Database |
+--------------------+
| information_schema |
| NODE1 |
| RJYY |
| hellodb |
| mysql |
| performance_schema |
| test |
+--------------------+
mysql> USE hellodb;
mysql> SHOW TABLES;
+-------------------+
| Tables_in_hellodb |
+-------------------+
| classes |
| coc |
| courses |
| scores |
| students |
| teachers |
| toc |
+-------------------+
1、在students表中，查询年龄大于25岁，且为男性的同学的名字和年龄；
mysql> SELECT Name,Age FROM students WHERE Age >25 AND Gender='M';
+--------------+-----+
| Name | Age |
+--------------+-----+
| Xie Yanke | 53 |
| Ding Dian | 32 |
| Yu Yutong | 26 |
| Shi Qing | 46 |
| Tian Boguang | 33 |
| Xu Xian | 27 |
| Sun Dasheng | 100 |
+--------------+-----+
2、以ClassID为分组依据，显示每组的平均年龄；
mysql> SELECT avg(age),ClassID FROM students WHERE ClassID IS NOT NULL GROUP BY ClassID ;
+----------+---------+
| avg(age) | ClassID |
+----------+---------+
| 20.5000 | 1 |
| 36.0000 | 2 |
| 20.2500 | 3 |
| 24.7500 | 4 |
| 46.0000 | 5 |
| 20.7500 | 6 |
| 19.6667 | 7 |
+----------+---------+
3、 显示第2题中平均年龄大于30的分组及平均年龄；
mysql> SELECT avg(Age),ClassID FROM students WHERE ClassID IS NOT NULL GROUP BY ClassID HAVING avg(Age) > 30;
+----------+---------+
| avg(Age) | ClassID |
+----------+---------+
| 36.0000 | 2 |
| 46.0000 | 5 |
+----------+---------+
4、显示以L开头的名字的同学的信息；
mysql> SELECT * FROM students WHERE Name LIKE 'L%';
+-------+-------------+-----+--------+---------+-----------+
| StuID | Name | Age | Gender | ClassID | TeacherID |
+-------+-------------+-----+--------+---------+-----------+
| 8 | Lin Daiyu | 17 | F | 7 | NULL |
| 14 | Lu Wushuang | 17 | F | 3 | NULL |
| 17 | Lin Chong | 25 | M | 4 | NULL |
+-------+-------------+-----+--------+---------+-----------+
5、显示TeacherID非空的同学的相关信息；
mysql> SELECT * FROM students WHERE TeacherID IS NOT NULL;
+-------+-------------+-----+--------+---------+-----------+
| StuID | Name | Age | Gender | ClassID | TeacherID |
+-------+-------------+-----+--------+---------+-----------+
| 1 | Shi Zhongyu | 22 | M | 2 | 3 |
| 2 | Shi Potian | 22 | M | 1 | 7 |
| 3 | Xie Yanke | 53 | M | 2 | 16 |
| 4 | Ding Dian | 32 | M | 4 | 4 |
| 5 | Yu Yutong | 26 | M | 3 | 1 |
+-------+-------------+-----+--------+---------+-----------+
6、以年龄排序后，显示年龄最大的前10位同学的信息；
mysql> SELECT * FROM students ORDER BY Age DESC LIMIT 10;
+-------+--------------+-----+--------+---------+-----------+
| StuID | Name | Age | Gender | ClassID | TeacherID |
+-------+--------------+-----+--------+---------+-----------+
| 25 | Sun Dasheng | 100 | M | NULL | NULL |
| 3 | Xie Yanke | 53 | M | 2 | 16 |
| 6 | Shi Qing | 46 | M | 5 | NULL |
| 13 | Tian Boguang | 33 | M | 2 | NULL |
| 4 | Ding Dian | 32 | M | 4 | 4 |
| 24 | Xu Xian | 27 | M | NULL | NULL |
| 5 | Yu Yutong | 26 | M | 3 | 1 |
| 17 | Lin Chong | 25 | M | 4 | NULL |
| 23 | Ma Chao | 23 | M | 4 | NULL |
| 18 | Hua Rong | 23 | M | 7 | NULL |
+-------+--------------+-----+--------+---------+-----------+
7、 查询年龄大于等于20岁，小于等于25岁的同学的信息；用三种方法；
mysql> SELECT * FROM students WHERE Age >=20 AND Age <=25;
mysql> SELECT * FROM students WHERE Age BETWEEN 20 AND 25;
mysql> SELECT * FROM students WHERE Age IN (20,21,22,23,24,25);
+-------+---------------+-----+--------+---------+-----------+
| StuID | Name | Age | Gender | ClassID | TeacherID |
+-------+---------------+-----+--------+---------+-----------+
| 1 | Shi Zhongyu | 22 | M | 2 | 3 |
| 2 | Shi Potian | 22 | M | 1 | 7 |
| 9 | Ren Yingying | 20 | F | 6 | NULL |
| 11 | Yuan Chengzhi | 23 | M | 6 | NULL |
| 16 | Xu Zhu | 21 | M | 1 | NULL |
| 17 | Lin Chong | 25 | M | 4 | NULL |
| 18 | Hua Rong | 23 | M | 7 | NULL |
| 21 | Huang Yueying | 22 | F | 6 | NULL |
| 22 | Xiao Qiao | 20 | F | 1 | NULL |
| 23 | Ma Chao | 23 | M | 4 | NULL |
+-------+---------------+-----+--------+---------+-----------+
二、 导入hellodb.sql，以下操作在students表上执行
1、以ClassID分组，显示每班的同学的人数；
mysql> SELECT count(StuID),ClassID FROM students GROUP BY ClassID ;
+--------------+---------+
| count(StuID) | ClassID |
+--------------+---------+
| 2 | NULL |
| 4 | 1 |
| 3 | 2 |
| 4 | 3 |
| 4 | 4 |
| 1 | 5 |
| 4 | 6 |
| 3 | 7 |
+--------------+---------+
2、以Gender分组，显示其年龄之和；
mysql> SELECT sum(Age),Gender FROM students GROUP BY Gender ;
+----------+--------+
| sum(Age) | Gender |
+----------+--------+
| 190 | F |
| 495 | M |
+----------+--------+
3、以ClassID分组，显示其平均年龄大于25的班级；
mysql> SELECT avg(Age),ClassID FROM students GROUP BY ClassID HAVING avg(Age) > 25;
+----------+---------+
| avg(Age) | ClassID |
+----------+---------+
| 63.5000 | NULL |
| 36.0000 | 2 |
| 46.0000 | 5 |
+----------+---------+
4、以Gender分组，显示各组中年龄大于25的学员的年龄之和；
mysql> SELECT sum(Age),Gender FROM students WHERE Age > 25 GROUP BY Gender ;
+----------+--------+
| sum(Age) | Gender |
+----------+--------+
| 317 | M |
+----------+--------+
三、导入hellodb.sql，完成以下题目：
1、显示前5位同学的姓名、课程及成绩；
mysql> SELECT s.Name,courses.Course,scores.Score FROM (select * from students limit 5)
AS s LEFT JOIN scores ON scores.StuID = s.StuID LEFT JOIN courses ON scores.CourseID =courses.CourseID;
mysql> SELECT s.name,sc.course,sc.score FROM (SELECT * FROM students LIMIT 5 )
AS s LEFT JOIN (SELECT scores.stuid,courses.course,scores.score FROM scores LEFT JOIN courses ON
courses.CourseID=scores.CourseID)AS sc ON s.StuId=sc.StuID;
+-------------+----------------+-------+
| name | course | score |
+-------------+----------------+-------+
| Shi Zhongyu | Kuihua Baodian | 77 |
| Shi Zhongyu | Weituo Zhang | 93 |
| Shi Potian | Kuihua Baodian | 47 |
| Shi Potian | Daiyu Zanghua | 97 |
| Xie Yanke | Kuihua Baodian | 88 |
| Xie Yanke | Weituo Zhang | 75 |
| Ding Dian | Daiyu Zanghua | 71 |
| Ding Dian | Kuihua Baodian | 89 |
| Yu Yutong | Hamo Gong | 39 |
| Yu Yutong | Dagou Bangfa | 63 |
+-------------+----------------+-------+
2、显示其成绩高于80的同学的名称及课程；
mysql> SELECT Name,Course,Score FROM (students LEFT JOIN scores ON students.StuID=scores.StuID )
LEFT JOIN courses ON courses.CourseID=scores.CourseID WHERE Score > 80;
+-------------+----------------+-------+
| Name | Course | Score |
+-------------+----------------+-------+
| Shi Zhongyu | Weituo Zhang | 93 |
| Shi Potian | Daiyu Zanghua | 97 |
| Xie Yanke | Kuihua Baodian | 88 |
| Ding Dian | Kuihua Baodian | 89 |
| Shi Qing | Hamo Gong | 96 |
| Xi Ren | Hamo Gong | 86 |
| Xi Ren | Dagou Bangfa | 83 |
| Lin Daiyu | Jinshe Jianfa | 93 |
+-------------+----------------+-------+
3、求前8位同学每位同学自己两门课的平均成绩，并按降序排列；
mysql> SELECT Name,avg(Score) FROM (SELECT * FROM students LIMIT 8) AS rj LEFT JOIN scores AS
jr ON rj.StuID=jr.StuID GROUP BY Name ORDER BY avg(Score) DESC;
+-------------+------------+
| Name | avg(Score) |
+-------------+------------+
| Shi Qing | 96.0000 |
| Shi Zhongyu | 85.0000 |
| Xi Ren | 84.5000 |
| Xie Yanke | 81.5000 |
| Ding Dian | 80.0000 |
| Lin Daiyu | 75.0000 |
| Shi Potian | 72.0000 |
| Yu Yutong | 51.0000 |
+-------------+------------+
4、显示每门课程课程名称及学习了这门课的同学的个数；
mysql> SELECT courses.Course,count(rj.StuID) FROM scores AS rj LEFT JOIN courses ON courses.CourseID=rj.CourseID GROUP BY rj.CourseID;
+----------------+-----------------+
| Course | count(rj.StuID) |
+----------------+-----------------+
| Hamo Gong | 3 |
| Kuihua Baodian | 4 |
| Jinshe Jianfa | 1 |
| Taiji Quan | 1 |
| Daiyu Zanghua | 2 |
| Weituo Zhang | 2 |
| Dagou Bangfa | 2 |
+----------------+-----------------+
四、思考题
1、如何显示其年龄大于平均年龄的同学的名字？
mysql> SELECT Name,Age FROM students WHERE Age > (SELECT avg(Age) FROM students);
+--------------+-----+
| Name | Age |
+--------------+-----+
| Xie Yanke | 53 |
| Ding Dian | 32 |
| Shi Qing | 46 |
| Tian Boguang | 33 |
| Sun Dasheng | 100 |
+--------------+-----+
2、如何显示其学习的课程为第1、2，4或第7门课的同学的名字？
mysql> SELECT rj.Name,scores.CourseID FROM students AS rj LEFT JOIN scores ON scores.StuID = rj.StuID WHERE scores.CourseID IN (1,2,4,7);
+-------------+----------+
| Name | CourseID |
+-------------+----------+
| Shi Zhongyu | 2 |
| Shi Potian | 2 |
| Xie Yanke | 2 |
| Ding Dian | 2 |
| Yu Yutong | 1 |
| Yu Yutong | 7 |
| Shi Qing | 1 |
| Xi Ren | 1 |
| Xi Ren | 7 |
| Lin Daiyu | 4 |
+-------------+----------+
3、如何显示其成员数最少为3个的班级的同学中年龄大于同班同学平均年龄的同学？
mysql> SELECT students.name,students.age,tp.classid,tp.vg FROM students,(SELECT classid,COUNT(stuid)
AS cs,AVG(age) AS vg FROM students GROUP BY classid HAVING cs >=3) AS tp WHERE students.age>tp.vg AND students.classid=tp.classid;
+---------------+-----+---------+---------+
| name | age | classid | vg |
+---------------+-----+---------+---------+
| Shi Potian | 22 | 1 | 20.5000 |
| Xie Yanke | 53 | 2 | 36.0000 |
| Ding Dian | 32 | 4 | 24.7500 |
| Yu Yutong | 26 | 3 | 20.2500 |
| Yuan Chengzhi | 23 | 6 | 20.7500 |
| Xu Zhu | 21 | 1 | 20.5000 |
| Lin Chong | 25 | 4 | 24.7500 |
| Hua Rong | 23 | 7 | 19.6667 |
| Huang Yueying | 22 | 6 | 20.7500 |
+---------------+-----+---------+---------+
4、统计各班级中年龄大于全校同学平均年龄的同学。
mysql> SELECT rj.Name,rj.Age FROM students AS rj LEFT JOIN classes AS jr ON
rj.ClassID=jr.ClassID WHERE rj.ClassID=jr.ClassID AND Age > (SELECT AVG(Age) FROM students);
+--------------+-----+
| Name | Age |
+--------------+-----+
| Xie Yanke | 53 |
| Ding Dian | 32 |
| Shi Qing | 46 |
| Tian Boguang | 33 |
+--------------+-----+