- 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
MariaDB [hellodb]> select name,age from students where age>25;
+--------------+-----+
| name | age |
+--------------+-----+
| Xie Yanke | 53 |
| Ding Dian | 32 |
| Yu Yutong | 26 |
| Shi Qing | 46 |
| Tian Boguang | 33 |
| Xu Xian | 27 |
| Sun Dasheng | 100 |
+--------------+-----+
7 rows in set (0.000 sec)
- 以ClassID为分组依据，显示每组的平均年龄
MariaDB [hellodb]> select classid,avg(age) from students group by classid ;
+---------+----------+
| classid | avg(age) |
+---------+----------+
| NULL | 63.5000 |
| 1 | 20.5000 |
| 2 | 36.0000 |
| 3 | 20.2500 |
| 4 | 24.7500 |
| 5 | 46.0000 |
| 6 | 20.7500 |
| 7 | 19.6667 |
+---------+----------+
- 显示第2题中平均年龄大于30的分组及平均年龄
MariaDB [hellodb]> select classid,avg(age) vage from students group by classid having vage>30;
+---------+---------+
| classid | vage |
+---------+---------+
| NULL | 63.5000 |
| 2 | 36.0000 |
| 5 | 46.0000 |
+---------+---------+
- 显示以L开头的名字的同学的信息
MariaDB [hellodb]> select name from students where name like ‘l%‘;
+-------------+
| name |
+-------------+
| Lin Daiyu |
| Lu Wushuang |
| Lin Chong |
+-------------+
3 rows in set (0.000 sec)
- 显示TeacherID非空的同学的相关信息
MariaDB [hellodb]> 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 |
+-------+-------------+-----+--------+---------+-----------+
5 rows in set (0.000 sec)
- 以年龄排序后，显示年龄最大的前10位同学的信息
MariaDB [hellodb]> select * from students order by age limit 10;
+-------+--------------+-----+--------+---------+-----------+
| StuID | Name | Age | Gender | ClassID | TeacherID |
+-------+--------------+-----+--------+---------+-----------+
| 14 | Lu Wushuang | 17 | F | 3 | NULL |
| 8 | Lin Daiyu | 17 | F | 7 | NULL |
| 19 | Xue Baochai | 18 | F | 6 | NULL |
| 15 | Duan Yu | 19 | M | 4 | NULL |
| 12 | Wen Qingqing | 19 | F | 1 | NULL |
| 7 | Xi Ren | 19 | F | 3 | NULL |
| 20 | Diao Chan | 19 | F | 7 | NULL |
| 10 | Yue Lingshan | 19 | F | 3 | NULL |
| 9 | Ren Yingying | 20 | F | 6 | NULL |
| 22 | Xiao Qiao | 20 | F | 1 | NULL |
+-------+--------------+-----+--------+---------+-----------+
10 rows in set (0.000 sec)
- 查询年龄大于等于20岁，小于等于25岁的同学的信息
MariaDB [hellodb]> select * from students where age>=20 and age<=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 |
+-------+---------------+-----+--------+---------+-----------+
10 rows in set (0.000 sec)
- 以ClassID分组，显示每班的同学的人数
MariaDB [hellodb]> select classid,count(classid) 人数 from students group by classid ;
+---------+--------+
| classid | 人数 |
+---------+--------+
| NULL | 0 |
| 1 | 4 |
| 2 | 3 |
| 3 | 4 |
| 4 | 4 |
| 5 | 1 |
| 6 | 4 |
| 7 | 3 |
+---------+--------+
8 rows in set (0.000 sec)
- 以Gender分组，显示其年龄之和
MariaDB [hellodb]> select sum(age),gender from students group by gender ;
+----------+--------+
| sum(age) | gender |
+----------+--------+
| 190 | F |
| 495 | M |
+----------+--------+
2 rows in set (0.000 sec)
- 以ClassID分组，显示其平均年龄大于25的班级
MariaDB [hellodb]> select classid,avg(age) 平均年纪 from students group by classid having 平均年纪>25;
+---------+--------------+
| classid | 平均年纪 |
+---------+--------------+
| NULL | 63.5000 |
| 2 | 36.0000 |
| 5 | 46.0000 |
+---------+--------------+
3 rows in set (0.001 sec)
- 以Gender分组，显示各组中年龄大于25的学员的年龄之和
MariaDB [hellodb]> select sum(age),gender from (select age,gender from students where age > 25) as s;
+----------+--------+
| sum(age) | gender |
+----------+--------+
| 317 | M |
+----------+--------+
1 row in set (0.000 sec)
- 显示前5位同学的姓名、课程及成绩
MariaDB [hellodb]> select st.stuid,st.name,co.course,sc.score from students st inner join scores sc on st.stuid=sc.stuid inner join courses co on sc.courseid=sc.courseid order by sc.score desc limit 5;
- 显示其成绩高于80的同学的名称及课程
MariaDB [hellodb]> select st.stuid,st.name,co.course,sc.score from students st inner join scores sc on st.stuid=sc.stuid inner join courses co on sc.courseid=sc.courseid and sc.score>80;
+-------+-------------+----------------+-------+
| stuid | name | course | score |
+-------+-------------+----------------+-------+
| 1 | Shi Zhongyu | Hamo Gong | 93 |
| 1 | Shi Zhongyu | Kuihua Baodian | 93 |
| 1 | Shi Zhongyu | Jinshe Jianfa | 93 |
| 1 | Shi Zhongyu | Taiji Quan | 93 |
| 1 | Shi Zhongyu | Daiyu Zanghua | 93 |
| 1 | Shi Zhongyu | Weituo Zhang | 93 |
| 1 | Shi Zhongyu | Dagou Bangfa | 93 |
| 2 | Shi Potian | Hamo Gong | 97 |
| 2 | Shi Potian | Kuihua Baodian | 97 |
| 2 | Shi Potian | Jinshe Jianfa | 97 |
| 2 | Shi Potian | Taiji Quan | 97 |
| 2 | Shi Potian | Daiyu Zanghua | 97 |
| 2 | Shi Potian | Weituo Zhang | 97 |
- 取每位同学各门课的平均成绩，显示成绩前三名的同学的姓名和平均成绩
MariaDB [hellodb]> select st.stuid,st.name,co.course,avg(sc.score) from students st inner join scores sc on st.stuid=sc.stuid inner join courses co on sc.courseid=sc.courseid group by st.name order by sc.score desc limit 3;
+-------+-----------+-----------+---------------+
| stuid | name | course | avg(sc.score) |
+-------+-----------+-----------+---------------+
| 6 | Shi Qing | Hamo Gong | 96.0000 |
| 3 | Xie Yanke | Hamo Gong | 81.5000 |
| 7 | Xi Ren | Hamo Gong | 84.5000 |
+-------+-----------+-----------+---------------+
- 显示每门课程课程名称及学习了这门课的同学的个数
MariaDB [hellodb]> select st.stuid,count(co.course) 报名人数,co.course 课程 from students st inner join scores sc on st.stuid=sc.stuid inner join courses co on sc.courseid=sc.courseid group by co.course;
+-------+--------------+----------------+
| stuid | 报名人数 | 课程 |
+-------+--------------+----------------+
| 1 | 15 | Dagou Bangfa |
| 1 | 15 | Daiyu Zanghua |
| 1 | 15 | Hamo Gong |
| 1 | 15 | Jinshe Jianfa |
| 1 | 15 | Kuihua Baodian |
| 1 | 15 | Taiji Quan |
| 1 | 15 | Weituo Zhang |
- 显示其年龄大于平均年龄的同学的名字
MariaDB [hellodb]> select age,name from students where age > ( select avg(age) from students);
+-----+--------------+
| age | name |
+-----+--------------+
| 53 | Xie Yanke |
| 32 | Ding Dian |
| 46 | Shi Qing |
| 33 | Tian Boguang |
| 100 | Sun Dasheng |
+-----+--------------+
- 显示其学习的课程为第1、2，4或第7门课的同学的名字
MariaDB [hellodb]> select st.stuid,st.name,co.course,co.courseid from students st inner join scores sc on st.stuid=sc.stuid inner join courses co on sc.courseid=sc.courseid and co.courseid in (1,2,4,7);
+-------+-------------+----------------+----------+
| stuid | name | course | courseid |
+-------+-------------+----------------+----------+
| 1 | Shi Zhongyu | Hamo Gong | 1 |
| 1 | Shi Zhongyu | Kuihua Baodian | 2 |
| 1 | Shi Zhongyu | Taiji Quan | 4 |
| 1 | Shi Zhongyu | Dagou Bangfa | 7 |
| 1 | Shi Zhongyu | Hamo Gong | 1 |
| 1 | Shi Zhongyu | Kuihua Baodian | 2 |
| 1 | Shi Zhongyu | Taiji Quan | 4 |
| 1 | Shi Zhongyu | Dagou Bangfa | 7 |
| 2 | Shi Potian | Hamo Gong | 1 |
- 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
#写不来 算是抄的
MariaDB [hellodb]> select age,name,g from students s1 inner join (select count(classid) cl,classid,avg(age) g from students group by classid having cl>=3) as s2 on s1.classid=s2.classid and s1.age>g;
+-----+---------------+---------+
| age | name | g |
+-----+---------------+---------+
| 22 | Shi Potian | 20.5000 |
| 53 | Xie Yanke | 36.0000 |
| 32 | Ding Dian | 24.7500 |
| 26 | Yu Yutong | 20.2500 |
| 23 | Yuan Chengzhi | 20.7500 |
| 21 | Xu Zhu | 20.5000 |
| 25 | Lin Chong | 24.7500 |
| 23 | Hua Rong | 19.6667 |
| 22 | Huang Yueying | 20.7500 |
+-----+---------------+---------+
- 统计各班级中年龄大于全校同学平均年龄的同学
MariaDB [hellodb]> 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 |
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