MySQL数据库练习【二】
MySQL数据库练习【二】
- 一、MySQL基本语法
- 二、建库建表-数据准备
- 三、MySQL经典50题-题目
- 四、MySQL经典50题-答案
-
- 4.1、查询"01"课程比"02"课程成绩高的学生的信息及课程分数
- 4.2、查询"01"课程比"02"课程成绩低的学生的信息及课程分数
- 4.3.0、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
- 4.3.1、总分超过200分的同学的学生编号和学生姓名和总成绩
- 4.4、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
- 4.5、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
- 4.6、查询"李"姓老师的数量
- 4.7、查询学过"张三"老师授课的同学的信息
- 4.8、查询没学过"张三"老师授课的同学的信息
- 4.9、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
- 4.10、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
- 4.11、查询没有学全所有课程的同学的信息
- 4.12、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
- 4.13.0、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
- 4.13.1、MySQL中，聚合函数GROUP_CONCAT()用指定分隔符连接字符串
- 4.14、查询没学过"张三"老师讲授的任一门课程的学生姓名
- 4.15、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
- 4.16、检索"01"课程分数小于60，按分数降序排列的学生信息
- 4.17.1、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
- 4.17.2、CASE WHEN函数
- 4.17.3、CASE WHEN函数使用
- 4.18、查询各科成绩最高分、最低分和平均分：
- 4.19、按各科成绩进行排序，并显示排名
- 4.20、查询学生的总成绩并进行排名
- 4.21、查询不同老师所教不同课程平均分从高到低显示
- 4.22、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
- 4.23、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
- 4.24、查询学生平均成绩及其名次
- 4.24.1、MySql中@符号的使用【经典】
- 4.25、查询各科成绩前三名的记录【经典】
- 4.26、查询每门课程被选修的学生数
- 4.27、查询出只有两门课程的全部学生的学号和姓名
- 4.28、查询男生、女生人数
- 4.29、查询名字中含有"风"字的学生信息
- 4.30、查询同名同性学生名单，并统计同名人数
- 4.31、查询1990年出生的学生名单
- 4.32、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
- 4.33、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
- 4.34、查询课程名称为"数学"，且分数低于60的学生姓名和分数
- 4.35、查询所有学生的课程及分数情况；
- 4.36、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
- 4.37、查询不及格的课程
- 4.38、查询课程编号为01且课程成绩在80分及以上的学生的学号和姓名
- 4.39、求每门课程的学生人数
- 4.40、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
- 4.41、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
- 4.42、查询每门功课成绩最好的前两名【经典】
- 4.43、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。
- 4.44、检索至少选修两门课程的学生学号
- 4.45、查询选修了全部课程的学生信息
- 4.46、查询各学生的年龄
- 4.47、查询本周过生日的学生
- 4.48、查询下周过生日的学生
- 4.49、查询本月过生日的学生
- 4.50、查询下月过生日的学生
- end
一、MySQL基本语法
-- 创建数据库时指定编码方式
create database students character set utf8;
-- 查看数据库
show databases;
-- 查看已经创建的数据库信息
show create database students;
-- 修改数据库的编码
alter database students default character set utf8;
-- 删除数据库
drop database students;
-- 查看数据表
show create table student;
-- 查看表结构
desc student;
-- 修改创建好的表名 将原来的表名改为stu
alter table student rename stu;
-- 修改表中字段 将原来的字段名name改为sname字段名
alter table stu change name sname char(10);
-- 添加字段 在stu表中添加一个age整形字段
alter table student add age int;
-- 删除字段 刚刚创建的age整形字段
alter table student drop age;
-- 删除表
drop table if exists student;
二、建库建表-数据准备
create database school;
use school;
--1.学生表
CREATE TABLE `student` (
`sid` varchar(10) NOT NULL COMMENT '学生编号',
`sname` varchar(20) NOT NULL COMMENT '学生姓名',
`sage` DATETIME NOT NULL COMMENT '出生年月',
`ssex` varchar(10) NOT NULL COMMENT '学生性别'
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='学生表';
INSERT INTO student VALUES('01' , '赵雷' , '1990-01-01' , '男'),('02' , '钱电' , '1990-12-21' , '男'),
('03' , '孙风' , '1990-05-20' , '男'),('04' , '李云' , '1990-08-06' , '男'),
('05' , '周梅' , '1991-12-01' , '女'),('06' , '吴兰' , '1992-03-01' , '女'),
('07' , '郑竹' , '1989-07-01' , '女'),('08' , '王菊' , '1990-01-20' , '女');
select * from student;
desc student;
--2.课程表
CREATE TABLE `course` (
`cid` varchar(10) NOT NULL COMMENT '课程编号',
`cname` varchar(10) NOT NULL COMMENT '课程名称',
`tid` varchar(10) NOT NULL COMMENT '教师编号'
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='课程表';
INSERT INTO course VALUES('01' , '语文' , '02'),('02' , '数学' , '01'),('03' , '英语' , '03');
select * from course;
desc course;
--3.教师表
CREATE TABLE `teacher` (
`tid` varchar(10) NOT NULL COMMENT '教师编号',
`tname` varchar(10) NOT NULL COMMENT '教师姓名'
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='教师表';
INSERT INTO teacher VALUES('01' , '张三'),('02' , '李四'),('03' , '王五');
select * from teacher;
desc teacher;
--4.成绩表
CREATE TABLE `sc` (
`sid` varchar(10) NOT NULL COMMENT '学生编号',
`cid` varchar(10) NOT NULL COMMENT '课程编号',
`score` DECIMAL(18,1) NOT NULL COMMENT '分数'
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='成绩表';
INSERT INTO sc VALUES('01' , '01' , 80),('01' , '02' , 90),('01' , '03' , 99),
('02' , '01' , 70),('02' , '02' , 60),('02' , '03' , 80),('03' , '01' , 80),
('03' , '02' , 80),('03' , '03' , 80),('04' , '01' , 50),('04' , '02' , 30),
('04' , '03' , 20),('05' , '01' , 76),('05' , '02' , 87),('06' , '01' , 31),
('06' , '03' , 34),('07' , '02' , 89),('07' , '03' , 98);
select * from sc;
desc sc;
| 学生表student | 成绩表sc | 课程表course | 教师表teacher |
|---|---|---|---|
sid：学生编号 |
sid：学生编号 |
cid：课程编号 |
tid：教师编号 |
| sname：学生姓名 | cid：课程编号 |
cname：课程名称 | tname：教师姓名 |
| sage：出生年月 | score：分数 | tid：教师编号 |
|
| ssex：学生性别 |
| sid | sname | sage | ssex |
|---|---|---|---|
| 01 | 赵雷 | 1990-01-01 00:00:00 | 男 |
| 02 | 钱电 | 1990-12-21 00:00:00 | 男 |
| 03 | 孙风 | 1990-05-20 00:00:00 | 男 |
| 04 | 李云 | 1990-08-06 00:00:00 | 男 |
| 05 | 周梅 | 1991-12-01 00:00:00 | 女 |
| 06 | 吴兰 | 1992-03-01 00:00:00 | 女 |
| 07 | 郑竹 | 1989-07-01 00:00:00 | 女 |
| 08 | 王菊 | 1990-01-20 00:00:00 | 女 |
| 09 | 李白 | 2024-02-08 00:00:00 | 男 |
| 10 | 玛利亚 | 2024-02-08 00:00:00 | 女 |
| sid | cid | score |
|---|---|---|
| 01 | 01 | 80.0 |
| 01 | 02 | 90.0 |
| 01 | 03 | 99.0 |
| 02 | 01 | 70.0 |
| 02 | 02 | 60.0 |
| 02 | 03 | 80.0 |
| 03 | 01 | 80.0 |
| 03 | 02 | 80.0 |
| 03 | 03 | 80.0 |
| 04 | 01 | 50.0 |
| 04 | 02 | 30.0 |
| 04 | 03 | 20.0 |
| 05 | 01 | 76.0 |
| 05 | 02 | 87.0 |
| 06 | 01 | 31.0 |
| 06 | 03 | 34.0 |
| 07 | 02 | 89.0 |
| 07 | 03 | 98.0 |
| cid | cname | tid |
|---|---|---|
| 01 | 语文 | 02 |
| 02 | 数学 | 01 |
| 03 | 英语 | 03 |
| tid | tname |
|---|---|
| 01 | 张三 |
| 02 | 李四 |
| 03 | 王五 |
三、MySQL经典50题-题目
4.1、查询"01"课程比"02"课程成绩高的学生的信息及课程分数
4.2、查询"01"课程比"02"课程成绩低的学生的信息及课程分数
4.3.0、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
4.3.1、总分超过200分的同学的学生编号和学生姓名和总成绩
4.4、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
4.5、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
4.6、查询"李"姓老师的数量
4.7、查询学过"张三"老师授课的同学的信息
4.8、查询没学过"张三"老师授课的同学的信息
4.9、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
4.10、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
4.11、查询没有学全所有课程的同学的信息
4.12、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
4.13.0、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
4.13.1、MySQL中，聚合函数GROUP_CONCAT()用指定分隔符连接字符串
4.14、查询没学过"张三"老师讲授的任一门课程的学生姓名
4.15、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
4.16、检索"01"课程分数小于60，按分数降序排列的学生信息
4.17.1、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
4.17.2、CASE WHEN函数
4.17.3、CASE WHEN函数使用
4.18、查询各科成绩最高分、最低分和平均分：
4.19、按各科成绩进行排序，并显示排名
4.20、查询学生的总成绩并进行排名
4.21、查询不同老师所教不同课程平均分从高到低显示
4.22、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
4.23、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
4.24、查询学生平均成绩及其名次
4.24.1、MySql中@符号的使用【经典】
4.25、查询各科成绩前三名的记录【经典】
4.26、查询每门课程被选修的学生数
4.27、查询出只有两门课程的全部学生的学号和姓名
4.28、查询男生、女生人数
4.29、查询名字中含有"风"字的学生信息
4.30、查询同名同性学生名单，并统计同名人数
4.31、查询1990年出生的学生名单
4.32、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
4.33、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
4.34、查询课程名称为"数学"，且分数低于60的学生姓名和分数
4.35、查询所有学生的课程及分数情况；
4.36、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
4.37、查询不及格的课程
4.38、查询课程编号为01且课程成绩在80分及以上的学生的学号和姓名
4.39、求每门课程的学生人数
4.40、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
4.41、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
4.42、查询每门功课成绩最好的前两名【经典】
4.43、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。
4.44、检索至少选修两门课程的学生学号
4.45、查询选修了全部课程的学生信息
4.46、查询各学生的年龄
4.47、查询本周过生日的学生
4.48、查询下周过生日的学生
4.49、查询本月过生日的学生
4.50、查询下月过生日的学生
四、MySQL经典50题-答案
4.1、查询"01"课程比"02"课程成绩高的学生的信息及课程分数
-- 学生表student、成绩表sc、课程表course、教师表teacher
-- 表结构：student、sc、course
-- 连接条件：student.sid=sc.sid
-- 先将课程为01和02的课程及对应分数筛选出来,再INNER JOIN,ON为01.sid = 02.sid,WHERE条件为01.score >02.score,结果'存'为新t3表
-- 再将student表和t3表INNER JOIN
SELECT student.*,t3.score FROM
(SELECT t1.sid,t1.score FROM
(SELECT sid,score FROM sc WHERE cid = "01") as t1
INNER JOIN (SELECT sid,score FROM sc WHERE cid = "02") as t2
ON t1.sid=t2.sid WHERE t1.score > t2.score
)as t3
INNER JOIN student
ON t3.sid = student.sid;
+-----+--------+---------------------+------+-------+
| sid | sname | sage | ssex | score |
+-----+--------+---------------------+------+-------+
| 02 | 钱电 | 1990-12-21 00:00:00 | 男 | 70.0 |
| 04 | 李云 | 1990-08-06 00:00:00 | 男 | 50.0 |
+-----+--------+---------------------+------+-------+
2 rows in set (0.00 sec)
select
stu.*,
s1.score '01课程分数',
s2.score '02课程分数'
from
student stu,
(select sid,score from sc where cid = '01') s1,
(select sid,score from sc where cid = '02') s2
where s1.score > s2.score -- 前者成绩高
and s1.sid = s2.sid
and s1.sid = stu.sid;
mysql> select
-> stu.*,
-> s1.score '01课程分数',
-> s2.score '02课程分数'
-> from
-> student stu,
-> (select sid,score from sc where cid = '01') s1,
-> (select sid,score from sc where cid = '02') s2
-> where s1.score > s2.score -- 前者成绩高
-> and s1.sid = s2.sid
-> and s1.sid = stu.sid;
+-----+--------+---------------------+------+----------------+----------------+
| SID | Sname | Sage | Ssex | 01课程分数 | 02课程分数 |
+-----+--------+---------------------+------+----------------+----------------+
| 02 | 钱电 | 1990-12-21 00:00:00 | 男 | 70.0 | 60.0 |
| 04 | 李云 | 1990-08-06 00:00:00 | 男 | 50.0 | 30.0 |
+-----+--------+---------------------+------+----------------+----------------+
2 rows in set (0.01 sec)
select
stu.*,
s1.score '01课程分数',
s2.score '02课程分数'
from
student stu,
sc s1,
sc s2
where s1.score > s2.score -- 前者成绩高
and s1.sid = s2.sid
and s1.cid = '01'
and s2.cid = '02'
and s1.sid = stu.sid;
mysql> select
-> stu.*,
-> s1.score '01课程分数',
-> s2.score '02课程分数'
-> from
-> student stu,
-> sc s1,
-> sc s2
-> where s1.score > s2.score -- 前者成绩高
-> and s1.sid = s2.sid
-> and s1.cid = '01'
-> and s2.cid = '02'
-> and s1.sid = stu.sid;
+-----+--------+---------------------+------+----------------+----------------+
| SID | Sname | Sage | Ssex | 01课程分数 | 02课程分数 |
+-----+--------+---------------------+------+----------------+----------------+
| 02 | 钱电 | 1990-12-21 00:00:00 | 男 | 70.0 | 60.0 |
| 04 | 李云 | 1990-08-06 00:00:00 | 男 | 50.0 | 30.0 |
+-----+--------+---------------------+------+----------------+----------------+
2 rows in set (0.00 sec)
select
stu.*,
s1.score '01课程分数',
s2.score '02课程分数'
from
student stu
inner join sc s1 on s1.sid = stu.sid and s1.cid = '01' -- 两个表通过学号连接，指定01
left join sc s2 on stu.sid = s2.sid and s2.cid = '02' or s2.cid = NULL -- 指定02，或者c中的c_id直接不存在
-- 为NULL的条件可以不存在，因为左连接中会直接排除c表中不存在的数据，包含NULL
where s1.score > s2.score; -- 判断条件
mysql> select
-> stu.*,
-> s1.score '01课程分数',
-> s2.score '02课程分数'
-> from
-> student stu
-> inner join sc s1 on s1.sid = stu.sid and s1.cid = '01' -- 两个表通过学号连接，指定01
-> left join sc s2 on stu.sid = s2.sid and s2.cid = '02' or s2.cid = NULL -- 指定02，或者c中的c_id直接不存在
-> -- 为NULL的条件可以不存在，因为左连接中会直接排除c表中不存在的数据，包含NULL
-> where s1.score > s2.score; -- 判断条件
+-----+--------+---------------------+------+----------------+----------------+
| SID | Sname | Sage | Ssex | 01课程分数 | 02课程分数 |
+-----+--------+---------------------+------+----------------+----------------+
| 02 | 钱电 | 1990-12-21 00:00:00 | 男 | 70.0 | 60.0 |
| 04 | 李云 | 1990-08-06 00:00:00 | 男 | 50.0 | 30.0 |
+-----+--------+---------------------+------+----------------+----------------+
2 rows in set (0.00 sec)
4.2、查询"01"课程比"02"课程成绩低的学生的信息及课程分数
select
stu.*,
s1.score '01课程分数',
s2.score '02课程分数'
from
student stu
left join sc s1 on stu.sid = s1.sid and s1.cid = '01' or s1.cid = NULL -- 包含NULL的数据
inner join sc s2 on stu.sid = s2.sid and s2.cid = '02'
where s1.score < s2.score;
mysql> select
-> stu.*,
-> s1.score '01课程分数',
-> s2.score '02课程分数'
-> from
-> student stu
-> left join sc s1 on stu.sid = s1.sid and s1.cid = '01' or s1.cid = NULL -- 包含NULL的数据
-> inner join sc s2 on stu.sid = s2.sid and s2.cid = '02'
-> where s1.score < s2.score;
+-----+--------+---------------------+------+----------------+----------------+
| SID | Sname | Sage | Ssex | 01课程分数 | 02课程分数 |
+-----+--------+---------------------+------+----------------+----------------+
| 01 | 赵雷 | 1990-01-01 00:00:00 | 男 | 80.0 | 90.0 |
| 05 | 周梅 | 1991-12-01 00:00:00 | 女 | 76.0 | 87.0 |
+-----+--------+---------------------+------+----------------+----------------+
2 rows in set (0.00 sec)
4.3.0、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
stu.sid '学生编号',
stu.sname '学生姓名',
round(avg(score),2) '平均成绩' -- round四舍五入函数
from student stu
inner join sc on stu.sid = sc.sid
group by stu.sid -- 根据sid进行分组,分组之后查询每个人的平均成绩
having avg(score) > 60; -- 先分组，后条件过滤
mysql> select
-> stu.sid '学生编号',
-> stu.sname '学生姓名',
-> round(avg(score),2) '平均成绩'
-> from student stu
-> inner join sc on stu.sid = sc.sid
-> group by stu.sid -- 根据sid进行分组,分组之后查询每个人的平均成绩
-> having avg(score) > 60; -- 先分组，后条件过滤
+--------------+--------------+--------------+
| 学生编号 | 学生姓名 | 平均成绩 |
+--------------+--------------+--------------+
| 01 | 赵雷 | 89.67 |
| 02 | 钱电 | 70.00 |
| 03 | 孙风 | 80.00 |
| 05 | 周梅 | 81.50 |
| 07 | 郑竹 | 93.50 |
+--------------+--------------+--------------+
5 rows in set (0.00 sec)
4.3.1、总分超过200分的同学的学生编号和学生姓名和总成绩
select
stu.sid '学生编号',
stu.sname '学生姓名',
round(sum(score),2) '总成绩'
from student stu
inner join sc on stu.sid = sc.sid
group by stu.sid
having(sum(score)) > 200;
mysql> select
-> stu.sid '学生编号',
-> stu.sname '学生姓名',
-> round(sum(score),2) '总成绩'
-> from student stu
-> inner join sc on stu.sid = sc.sid
-> group by stu.sid
-> having(sum(score)) > 200;
+--------------+--------------+-----------+
| 学生编号 | 学生姓名 | 总成绩 |
+--------------+--------------+-----------+
| 01 | 赵雷 | 269.00 |
| 02 | 钱电 | 210.00 |
| 03 | 孙风 | 240.00 |
+--------------+--------------+-----------+
3 rows in set (0.00 sec)
4.4、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
stu.sid '学生编号',
stu.sname '学生姓名',
round(avg(score)) '平均成绩'
from student stu
inner join sc on stu.sid = sc.sid
group by stu.sid
having avg(score) < 60;
mysql> select
-> stu.sid '学生编号',
-> stu.sname '学生姓名',
-> round(avg(score)) '平均成绩'
-> from student stu
-> inner join sc on stu.sid = sc.sid
-> group by stu.sid
-> having avg(score) < 60;
+--------------+--------------+--------------+
| 学生编号 | 学生姓名 | 平均成绩 |
+--------------+--------------+--------------+
| 04 | 李云 | 33 |
| 06 | 吴兰 | 33 |
+--------------+--------------+--------------+
2 rows in set (0.00 sec)
王菊成绩表中无数据
select distinct sid from sc; -- 查询所有学号
select
stu.sid '学生编号',
stu.sname '学生姓名',
0 '平均成绩'
from student stu
where stu.sid not in (select distinct sid from sc); -- 学生的学号不在表中
mysql> select
-> stu.sid '学生编号',
-> stu.sname '学生姓名',
-> 0 '平均成绩'
-> from student stu
-> where stu.sid not in (select distinct sid from sc); -- 学生的学号不在表中
+--------------+--------------+--------------+
| 学生编号 | 学生姓名 | 平均成绩 |
+--------------+--------------+--------------+
| 08 | 王菊 | 0 |
+--------------+--------------+--------------+
1 row in set (0.00 sec)
select
stu.sid '学生编号',
stu.sname '学生姓名',
round(avg(score)) '平均成绩'
from student stu
inner join sc on stu.sid = sc.sid
group by stu.sid
having avg(score) < 60
union -- 连接两张表
select
stu.sid '学生编号',
stu.sname '学生姓名',
0 '平均成绩'
from student stu
where stu.sid not in (select distinct sid from sc); -- 学生的学号不在表中
mysql> select
-> stu.sid '学生编号',
-> stu.sname '学生姓名',
-> round(avg(score)) '平均成绩'
-> from student stu
-> inner join sc on stu.sid = sc.sid
-> group by stu.sid
-> having avg(score) < 60
-> union -- 连接两张表
-> select
-> stu.sid '学生编号',
-> stu.sname '学生姓名',
-> 0 '平均成绩'
-> from student stu
-> where stu.sid not in (select distinct sid from sc); -- 学生的学号不在表中
+--------------+--------------+--------------+
| 学生编号 | 学生姓名 | 平均成绩 |
+--------------+--------------+--------------+
| 04 | 李云 | 33 |
| 06 | 吴兰 | 33 |
| 08 | 王菊 | 0 |
+--------------+--------------+--------------+
3 rows in set (0.00 sec)
select
stu.sid '学生编号',
stu.sname '学生姓名',
round(avg(ifnull(sc.score,0))) '平均成绩'
from student stu
inner join sc on stu.sid = sc.sid
group by stu.sid
having avg(sc.score) < 60;
mysql> select
-> stu.sid '学生编号',
-> stu.sname '学生姓名',
-> round(avg(ifnull(sc.score,0))) '平均成绩'
-> from student stu
-> inner join sc on stu.sid = sc.sid
-> group by stu.sid
-> having avg(sc.score) < 60;
+--------------+--------------+--------------+
| 学生编号 | 学生姓名 | 平均成绩 |
+--------------+--------------+--------------+
| 04 | 李云 | 33 |
| 06 | 吴兰 | 33 |
+--------------+--------------+--------------+
2 rows in set (0.00 sec)
4.5、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
select
stu.sid '学生编号',
stu.sname '学生姓名',
count(sc.sid) '选课总数',
sum(sc.score) '总成绩'
from student stu
left join sc on stu.sid = sc.sid
group by stu.sid;
mysql> select
-> stu.sid '学生编号',
-> stu.sname '学生姓名',
-> count(sc.sid) '选课总数',
-> sum(sc.score) '总成绩'
-> from student stu
-> left join sc on stu.sid = sc.sid
-> group by stu.sid;
+--------------+--------------+--------------+-----------+
| 学生编号 | 学生姓名 | 选课总数 | 总成绩 |
+--------------+--------------+--------------+-----------+
| 01 | 赵雷 | 3 | 269.0 |
| 02 | 钱电 | 3 | 210.0 |
| 03 | 孙风 | 3 | 240.0 |
| 04 | 李云 | 3 | 100.0 |
| 05 | 周梅 | 2 | 163.0 |
| 06 | 吴兰 | 2 | 65.0 |
| 07 | 郑竹 | 2 | 187.0 |
| 08 | 王菊 | 0 | NULL |
+--------------+--------------+--------------+-----------+
8 rows in set (0.00 sec)
4.6、查询"李"姓老师的数量
select
count(t.tname)
from teacher t
where t.tname like '李%'; -- 通配符
mysql> select
-> count(t.tname)
-> from teacher t
-> where t.tname like '李%'; -- 通配符
+----------------+
| count(t.tname) |
+----------------+
| 1 |
+----------------+
1 row in set (0.00 sec)
select
t.tname,
count(t.tname)
from teacher t
where left(t.tname,1) in ('李'); -- left函数
mysql> select
-> t.tname,
-> count(t.tname)
-> from teacher t
-> where left(t.tname,1) in ('李'); -- left函数
+--------+----------------+
| tname | count(t.tname) |
+--------+----------------+
| 李四 | 1 |
+--------+----------------+
1 row in set (0.00 sec)
4.7、查询学过"张三"老师授课的同学的信息
-- 查询课程cid
select cid
from teacher,course
where teacher.tid = course.tid and teacher.tname = '张三';
select
stu.*
from student stu,sc
where stu.sid = sc.sid
and sc.cid in (
select cid
from teacher,course
where teacher.tid = course.tid and teacher.tname = '张三');
mysql> select
-> stu.*
-> from student stu,sc
-> where stu.sid = sc.sid
-> and sc.cid in (
-> select cid
-> from teacher,course
-> where teacher.tid = course.tid and teacher.tname = '张三');
+-----+--------+---------------------+------+
| sid | sname | sage | ssex |
+-----+--------+---------------------+------+
| 01 | 赵雷 | 1990-01-01 00:00:00 | 男 |
| 02 | 钱电 | 1990-12-21 00:00:00 | 男 |
| 03 | 孙风 | 1990-05-20 00:00:00 | 男 |
| 04 | 李云 | 1990-08-06 00:00:00 | 男 |
| 05 | 周梅 | 1991-12-01 00:00:00 | 女 |
| 07 | 郑竹 | 1989-07-01 00:00:00 | 女 |
+-----+--------+---------------------+------+
6 rows in set (0.00 sec)
select stu.*
from teacher t
left join course c on t.tid = c.tid -- 课程表和教师表
left join sc on c.cid = sc.cid -- 成绩表和课程表
left join student stu on sc.sid = stu.sid -- 学生表和成绩表
where t.tname = '张三';
mysql> select stu.*
-> from teacher t
-> left join course c on t.tid = c.tid -- 课程表和教师表
-> left join sc on c.cid = sc.cid -- 成绩表和课程表
-> left join student stu on sc.sid = stu.sid -- 学生表和成绩表
-> where t.tname = '张三';
+------+--------+---------------------+------+
| sid | sname | sage | ssex |
+------+--------+---------------------+------+
| 01 | 赵雷 | 1990-01-01 00:00:00 | 男 |
| 02 | 钱电 | 1990-12-21 00:00:00 | 男 |
| 03 | 孙风 | 1990-05-20 00:00:00 | 男 |
| 04 | 李云 | 1990-08-06 00:00:00 | 男 |
| 05 | 周梅 | 1991-12-01 00:00:00 | 女 |
| 07 | 郑竹 | 1989-07-01 00:00:00 | 女 |
+------+--------+---------------------+------+
6 rows in set (0.00 sec)
4.8、查询没学过"张三"老师授课的同学的信息
select distinct sc.sid
from teacher t
left join course c on t.tid = c.tid
left join sc on c.cid = sc.cid
where t.tname = '张三';
select stu.*
from student stu
where sid not in (
select distinct sc.sid
from teacher t
left join course c on t.tid = c.tid
left join sc on c.cid = sc.cid
where t.tname = '张三');
mysql> select stu.*
-> from student stu
-> where sid not in (
-> select distinct sc.sid
-> from teacher t
-> left join course c on t.tid = c.tid
-> left join sc on c.cid = sc.cid
-> where t.tname = '张三');
+-----+--------+---------------------+------+
| sid | sname | sage | ssex |
+-----+--------+---------------------+------+
| 06 | 吴兰 | 1992-03-01 00:00:00 | 女 |
| 08 | 王菊 | 1990-01-20 00:00:00 | 女 |
+-----+--------+---------------------+------+
2 rows in set (0.00 sec)
4.9、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 s1.sid
from sc s1
inner join sc s2 on s1.sid = s2.sid
where s1.cid = '01' and s2.cid = '02';
select stu.*
from student stu
where stu.sid in (
select s1.sid
from sc s1
inner join sc s2 on s1.sid = s2.sid
where s1.cid = '01' and s2.cid = '02');
mysql> select stu.*
-> from student stu
-> where stu.sid in (
-> select s1.sid
-> from sc s1
-> inner join sc s2 on s1.sid = s2.sid
-> where s1.cid = '01' and s2.cid = '02');
+-----+--------+---------------------+------+
| sid | sname | sage | ssex |
+-----+--------+---------------------+------+
| 01 | 赵雷 | 1990-01-01 00:00:00 | 男 |
| 02 | 钱电 | 1990-12-21 00:00:00 | 男 |
| 03 | 孙风 | 1990-05-20 00:00:00 | 男 |
| 04 | 李云 | 1990-08-06 00:00:00 | 男 |
| 05 | 周梅 | 1991-12-01 00:00:00 | 女 |
+-----+--------+---------------------+------+
5 rows in set (0.00 sec)
select stu.*
from student stu,sc s1,sc s2
where s1.sid = s2.sid
and stu.sid = s1.sid
and s1.cid = '01'
and s2.cid = '02';
mysql> select stu.*
-> from student stu,sc s1,sc s2
-> where s1.sid = s2.sid
-> and stu.sid = s1.sid
-> and s1.cid = '01'
-> and s2.cid = '02';
+-----+--------+---------------------+------+
| sid | sname | sage | ssex |
+-----+--------+---------------------+------+
| 01 | 赵雷 | 1990-01-01 00:00:00 | 男 |
| 02 | 钱电 | 1990-12-21 00:00:00 | 男 |
| 03 | 孙风 | 1990-05-20 00:00:00 | 男 |
| 04 | 李云 | 1990-08-06 00:00:00 | 男 |
| 05 | 周梅 | 1991-12-01 00:00:00 | 女 |
+-----+--------+---------------------+------+
5 rows in set (0.00 sec)
4.10、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
-- 查询学过02课程的学生sid
select sid from sc where sc.cid = '02';
select sid
from sc
where sc.cid = '01' -- 修过01课程的学号
and sc.sid not in (select sid from sc where sc.cid = '02'); -- 同时学号不能在修过02课程中出现
select stu.*
from student stu
where stu.sid in(
select sid
from sc
where sc.cid = '01'
and sc.sid not in (select sid from sc where sc.cid = '02')
);
mysql> select stu.*
-> from student stu
-> where stu.sid in(
-> select sid
-> from sc
-> where sc.cid = '01'
-> and sc.sid not in (select sid from sc where sc.cid = '02')
-> );
+-----+--------+---------------------+------+
| sid | sname | sage | ssex |
+-----+--------+---------------------+------+
| 06 | 吴兰 | 1992-03-01 00:00:00 | 女 |
+-----+--------+---------------------+------+
1 row in set (0.00 sec)
4.11、查询没有学全所有课程的同学的信息
select stu.*
from student stu
left join sc on stu.sid = sc.sid
group by stu.sid -- 学号分组
having count(sc.cid) < (select count(*) from course); -- 筛选分组后学生的课程数<3
mysql> select stu.*
-> from student stu
-> left join sc on stu.sid = sc.sid
-> group by stu.sid -- 学号分组
-> having count(sc.cid) < (select count(*) from course); -- 筛选分组后学生的课程数<3
+-----+--------+---------------------+------+
| sid | sname | sage | ssex |
+-----+--------+---------------------+------+
| 05 | 周梅 | 1991-12-01 00:00:00 | 女 |
| 06 | 吴兰 | 1992-03-01 00:00:00 | 女 |
| 07 | 郑竹 | 1989-07-01 00:00:00 | 女 |
| 08 | 王菊 | 1990-01-20 00:00:00 | 女 |
+-----+--------+---------------------+------+
4 rows in set (0.00 sec)
select sc.sid
from sc
group by sc.sid
having count(sc.cid) = (select count(*) from course);
mysql> select sc.sid
-> from sc
-> group by sc.sid
-> having count(sc.cid) = (select count(*) from course);
+-----+
| sid |
+-----+
| 01 |
| 02 |
| 03 |
| 04 |
+-----+
4 rows in set (0.00 sec)
select stu.*
from student stu
where stu.sid not in (
select sc.sid
from sc
group by sc.sid
having count(sc.cid) = (select count(*) from course));
mysql> select stu.*
-> from student stu
-> where stu.sid not in (
-> select sc.sid
-> from sc
-> group by sc.sid
-> having count(sc.cid) = (select count(*) from course));
+-----+--------+---------------------+------+
| sid | sname | sage | ssex |
+-----+--------+---------------------+------+
| 05 | 周梅 | 1991-12-01 00:00:00 | 女 |
| 06 | 吴兰 | 1992-03-01 00:00:00 | 女 |
| 07 | 郑竹 | 1989-07-01 00:00:00 | 女 |
| 08 | 王菊 | 1990-01-20 00:00:00 | 女 |
+-----+--------+---------------------+------+
4 rows in set (0.00 sec)
4.12、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
-- 查询01号同学的所学课程cid
select sc.cid from sc where sc.sid = '01';
select stu.*
from student stu
inner join sc on stu.sid = sc.sid -- 学生表和成绩表的关联
and sc.cid in (select sc.cid from sc where sc.sid = '01') -- 对课程进行限制，只在01学生的课程内
group by stu.sid; -- 根据学号进行分组
mysql> select stu.*
-> from student stu
-> inner join sc on stu.sid = sc.sid -- 学生表和成绩表的关联
-> and sc.cid in (select sc.cid from sc where sc.sid = '01') -- 对课程进行限制，只在01学生的课程内
-> group by stu.sid; -- 根据学号进行分组
+-----+--------+---------------------+------+
| sid | sname | sage | ssex |
+-----+--------+---------------------+------+
| 01 | 赵雷 | 1990-01-01 00:00:00 | 男 |
| 02 | 钱电 | 1990-12-21 00:00:00 | 男 |
| 03 | 孙风 | 1990-05-20 00:00:00 | 男 |
| 04 | 李云 | 1990-08-06 00:00:00 | 男 |
| 05 | 周梅 | 1991-12-01 00:00:00 | 女 |
| 06 | 吴兰 | 1992-03-01 00:00:00 | 女 |
| 07 | 郑竹 | 1989-07-01 00:00:00 | 女 |
+-----+--------+---------------------+------+
7 rows in set (0.00 sec)
4.13.0、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
-- 查询01号同学学习的课程cid
select sc.cid from sc where sc.sid = '01';
-- 查询01号同学学习的课程cid总数
select count(sc.cid) from sc where sc.sid = '01';
select stu.*
from student stu
inner join sc on stu.sid = sc.sid
and sc.cid in (select sc.cid from sc where sc.sid = '01') -- 和01同学课程相同
and sc.sid != '01' -- 排除自身
group by stu.sid -- 根据sid进行分组
having (select count(sc.cid) from sc where sc.sid = stu.sid) = -- 和01同学所学课程总数相同
(select count(sc.cid) from sc where sc.sid = '01');
mysql> select stu.*
-> from student stu
-> inner join sc on stu.sid = sc.sid
-> and sc.cid in (select sc.cid from sc where sc.sid = '01') -- 和01同学课程相同
-> and sc.sid != '01' -- 排除自身
-> group by stu.sid -- 根据sid进行分组
-> having (select count(sc.cid) from sc where sc.sid = stu.sid) = -- 和01同学所学课程总数相同
-> (select count(sc.cid) from sc where sc.sid = '01');
+-----+--------+---------------------+------+
| sid | sname | sage | ssex |
+-----+--------+---------------------+------+
| 02 | 钱电 | 1990-12-21 00:00:00 | 男 |
| 03 | 孙风 | 1990-05-20 00:00:00 | 男 |
| 04 | 李云 | 1990-08-06 00:00:00 | 男 |
+-----+--------+---------------------+------+
3 rows in set (0.00 sec)
4.13.1、MySQL中，聚合函数GROUP_CONCAT()用指定分隔符连接字符串
-- 语法
group_concat([DISTINCT] 要连接的字段 [Order BY ASC/DESC 排序字段] [Separator '分隔符'])
select sid,group_concat(cid order by cid)
from sc
group by sid;
mysql> select sid,group_concat(cid order by cid)
-> from sc
-> group by sid;
+-----+--------------------------------+
| sid | group_concat(cid order by cid) |
+-----+--------------------------------+
| 01 | 01,02,03 |
| 02 | 01,02,03 |
| 03 | 01,02,03 |
| 04 | 01,02,03 |
| 05 | 01,02 |
| 06 | 01,03 |
| 07 | 02,03 |
+-----+--------------------------------+
7 rows in set (0.00 sec)
select sid
from sc
group by sid
having group_concat(cid order by cid) = ( -- 找出和01号学生分组合并结果相同的学号sid
select group_concat(cid order by cid) -- 01号学生分组合并，同时进行排序
from sc
group by sid
having sid = '01')
and sid != '01'; -- 排除01号同学
mysql> select sid
-> from sc
-> group by sid
-> having group_concat(cid order by cid) = (
-> select group_concat(cid order by cid)
-> from sc
-> group by sid
-> having sid = '01')
-> and sid != '01';
+-----+
| sid |
+-----+
| 02 |
| 03 |
| 04 |
+-----+
3 rows in set (0.00 sec)
4.14、查询没学过"张三"老师讲授的任一门课程的学生姓名
-- 查询张三老师的课程cid
select cid
from course s
inner join teacher t on s.tid = t.tid and t.tname = '张三';
-- 查询学过张三老师课程的学生sid
select sid
from sc
where cid in (
select cid
from course s
inner join teacher t on s.tid = t.tid and t.tname = '张三');
select stu.*
from student stu
where stu.sid not in (
select sid from sc where cid in (
select cid from course s inner join teacher t on s.tid = t.tid and t.tname = '张三')
);
mysql> select stu.*
-> from student stu
-> where stu.sid not in (
-> select sid from sc where cid in (
-> select cid from course s inner join teacher t on s.tid = t.tid and t.tname = '张三')
-> );
+-----+--------+---------------------+------+
| sid | sname | sage | ssex |
+-----+--------+---------------------+------+
| 06 | 吴兰 | 1992-03-01 00:00:00 | 女 |
| 08 | 王菊 | 1990-01-20 00:00:00 | 女 |
+-----+--------+---------------------+------+
2 rows in set (0.00 sec)
4.15、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
-- 查询成绩不合格同学的学号
select sid
from sc
where score < 60 -- 小于60分，不及格
group by sid
having count(*) >= 2; -- 不及格两门以上
select stu.sname,stu.sid,round(avg(score),2)
from student stu
left join sc on stu.sid = sc.sid
where stu.sid in (
select sid
from sc
where score < 60
group by sid
having count(*) >= 2)
group by stu.sid;
mysql> select stu.sname,stu.sid,round(avg(score),2)
-> from student stu
-> left join sc on stu.sid = sc.sid
-> where stu.sid in (
-> select sid
-> from sc
-> where score < 60
-> group by sid
-> having count(*) >= 2)
-> group by stu.sid;
+--------+-----+---------------------+
| sname | sid | round(avg(score),2) |
+--------+-----+---------------------+
| 李云 | 04 | 33.33 |
| 吴兰 | 06 | 32.50 |
+--------+-----+---------------------+
2 rows in set (0.00 sec)
select stu.sname,sc.sid,round(avg(score),2)
from sc
inner join student stu on sc.sid = stu.sid
where sc.score < 60
group by sc.sid
having count(sc.score) >= 2;
mysql> select stu.sname,sc.sid,round(avg(score),2)
-> from sc
-> inner join student stu on sc.sid = stu.sid
-> where sc.score < 60
-> group by sc.sid
-> having count(sc.score) >= 2;
+--------+-----+---------------------+
| sname | sid | round(avg(score),2) |
+--------+-----+---------------------+
| 李云 | 04 | 33.33 |
| 吴兰 | 06 | 32.50 |
+--------+-----+---------------------+
2 rows in set (0.00 sec)
select stu.sid,stu.sname,round(avg(score),2)
from student stu
inner join sc on stu.sid = sc.sid and sc.score < 60 -- 内连接且分数小于60
group by stu.sid -- 根据sid分组
having count(sc.sid) >= 2; -- 两门课
mysql> select stu.sid,stu.sname,round(avg(score),2)
-> from student stu
-> inner join sc on stu.sid = sc.sid and sc.score < 60 -- 内连接且分数小于60
-> group by stu.sid -- 根据sid分组
-> having count(sc.sid) >= 2; -- 两门课
+-----+--------+---------------------+
| sid | sname | round(avg(score),2) |
+-----+--------+---------------------+
| 04 | 李云 | 33.33 |
| 06 | 吴兰 | 32.50 |
+-----+--------+---------------------+
2 rows in set (0.00 sec)
4.16、检索"01"课程分数小于60，按分数降序排列的学生信息
select stu.*,sc.score
from student stu
left join sc on stu.sid = sc.sid
where sc.cid = '01' and sc.score < 60
order by score desc;
mysql> select stu.*,sc.score
-> from student stu
-> left join sc on stu.sid = sc.sid
-> where sc.cid = '01' and sc.score < 60
-> order by score desc;
+-----+--------+---------------------+------+-------+
| sid | sname | sage | ssex | score |
+-----+--------+---------------------+------+-------+
| 04 | 李云 | 1990-08-06 00:00:00 | 男 | 50.0 |
| 06 | 吴兰 | 1992-03-01 00:00:00 | 女 | 31.0 |
+-----+--------+---------------------+------+-------+
2 rows in set (0.01 sec)
4.17.1、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
-- 查询每位同学平均成绩，并降序
select sc.sid,avg(score) from sc group by sc.sid order by avg(score) desc;
select
s.sid,
(select sname from student where student.sid = s.sid) '姓名',
(select score from sc where sc.sid = s.sid and sc.cid = '01') '语文',
(select score from sc where sc.sid = s.sid and sc.cid = '02') '数学',
(select score from sc where sc.sid = s.sid and sc.cid = '03') '英语',
round(avg(s.score),2) '平均成绩'
from sc s
group by s.sid
order by avg(s.score) desc;
mysql> select
-> s.sid,
-> (select sname from student where student.sid = s.sid) '姓名',
-> (select score from sc where sc.sid = s.sid and sc.cid = '01') '语文',
-> (select score from sc where sc.sid = s.sid and sc.cid = '02') '数学',
-> (select score from sc where sc.sid = s.sid and sc.cid = '03') '英语',
-> round(avg(s.score),2) '平均成绩'
-> from sc s
-> group by s.sid
-> order by avg(s.score) desc;
+-----+--------+--------+--------+--------+--------------+
| sid | 姓名 | 语文 | 数学 | 英语 | 平均成绩 |
+-----+--------+--------+--------+--------+--------------+
| 07 | 郑竹 | NULL | 89.0 | 98.0 | 93.50 |
| 01 | 赵雷 | 80.0 | 90.0 | 99.0 | 89.67 |
| 05 | 周梅 | 76.0 | 87.0 | NULL | 81.50 |
| 03 | 孙风 | 80.0 | 80.0 | 80.0 | 80.00 |
| 02 | 钱电 | 70.0 | 60.0 | 80.0 | 70.00 |
| 04 | 李云 | 50.0 | 30.0 | 20.0 | 33.33 |
| 06 | 吴兰 | 31.0 | NULL | 34.0 | 32.50 |
+-----+--------+--------+--------+--------+--------------+
7 rows in set (0.00 sec)
没有第八号学生
4.17.2、CASE WHEN函数
CASE SCORE WHEN 'A' THEN '优' ELSE '不及格' END
-- THEN后边的值与ELSE后边的值类型应一致，否则会报错
-- 使用 IF 函数进行替换
IF(SCORE = 'A', '优', '不及格')
-- CASE WHEN条件表达式函数
CASE WHEN condition THEN result
[WHEN...THEN...]
ELSE result
END
CASE
WHEN SCORE > 90 THEN '优'
WHEN SCORE > 70 THEN '良'
WHEN SCORE > 60 THEN '中'
ELSE '不及格' END
4.17.3、CASE WHEN函数使用
select
stu.sname,
sc.sid,
sum(case when sc.cid = '01' then ifnull(sc.score,0) else 0 end) '语文',
sum(case when sc.cid = '02' then ifnull(sc.score,0) else 0 end) '数学',
sum(case when sc.cid = '03' then ifnull(sc.score,0) else 0 end) '英语',
round(avg(sc.score),2) '平均成绩'
from sc
left join student stu on sc.sid = stu.sid
group by sc.sid
union
select stu.sname,stu.sid,0 '语文',0 '数学',0 '英语',0 '平均成绩'
from student stu
where stu.sid not in (select distinct sid from sc)
order by 6 desc;
mysql> select
-> stu.sname,
-> sc.sid,
-> sum(case when sc.cid = '01' then ifnull(sc.score,0) else 0 end) '语文',
-> sum(case when sc.cid = '02' then ifnull(sc.score,0) else 0 end) '数学',
-> sum(case when sc.cid = '03' then ifnull(sc.score,0) else 0 end) '英语',
-> round(avg(sc.score),2) '平均成绩'
-> from sc
-> left join student stu on sc.sid = stu.sid
-> group by sc.sid
-> union
-> select stu.sname,stu.sid,0 '语文',0 '数学',0 '英语',0 '平均成绩'
-> from student stu
-> where stu.sid not in (select distinct sid from sc)
-> order by 6 desc;
+--------+-----+--------+--------+--------+--------------+
| sname | sid | 语文 | 数学 | 英语 | 平均成绩 |
+--------+-----+--------+--------+--------+--------------+
| 郑竹 | 07 | 0.0 | 89.0 | 98.0 | 93.50 |
| 赵雷 | 01 | 80.0 | 90.0 | 99.0 | 89.67 |
| 周梅 | 05 | 76.0 | 87.0 | 0.0 | 81.50 |
| 孙风 | 03 | 80.0 | 80.0 | 80.0 | 80.00 |
| 钱电 | 02 | 70.0 | 60.0 | 80.0 | 70.00 |
| 李云 | 04 | 50.0 | 30.0 | 20.0 | 33.33 |
| 吴兰 | 06 | 31.0 | 0.0 | 34.0 | 32.50 |
| 王菊 | 08 | 0.0 | 0.0 | 0.0 | 0.00 |
+--------+-----+--------+--------+--------+--------------+
8 rows in set (0.00 sec)
有第八号学生
select
stu.sname,
stu.sid,
s1.score '语文',
s2.score '数学',
s3.score '英语',
round(avg(s.score),2) '平均成绩'
from student stu
left join sc s on stu.sid = s.sid
left join sc s1 on s.sid = s1.sid and s1.cid = '01'
left join sc s2 on s.sid = s2.sid and s2.cid = '02'
left join sc s3 on s.sid = s3.sid and s3.cid = '03'
group by stu.sid
order by 6 desc;
mysql> select
-> stu.sname,
-> stu.sid,
-> s1.score '语文',
-> s2.score '数学',
-> s3.score '英语',
-> round(avg(s.score),2) '平均成绩'
-> from student stu
-> left join sc s on stu.sid = s.sid
-> left join sc s1 on s.sid = s1.sid and s1.cid = '01'
-> left join sc s2 on s.sid = s2.sid and s2.cid = '02'
-> left join sc s3 on s.sid = s3.sid and s3.cid = '03'
-> group by stu.sid
-> order by 6 desc;
+--------+-----+--------+--------+--------+--------------+
| sname | sid | 语文 | 数学 | 英语 | 平均成绩 |
+--------+-----+--------+--------+--------+--------------+
| 郑竹 | 07 | NULL | 89.0 | 98.0 | 93.50 |
| 赵雷 | 01 | 80.0 | 90.0 | 99.0 | 89.67 |
| 周梅 | 05 | 76.0 | 87.0 | NULL | 81.50 |
| 孙风 | 03 | 80.0 | 80.0 | 80.0 | 80.00 |
| 钱电 | 02 | 70.0 | 60.0 | 80.0 | 70.00 |
| 李云 | 04 | 50.0 | 30.0 | 20.0 | 33.33 |
| 吴兰 | 06 | 31.0 | NULL | 34.0 | 32.50 |
| 王菊 | 08 | NULL | NULL | NULL | NULL |
+--------+-----+--------+--------+--------+--------------+
8 rows in set (0.00 sec)
-- 非空判断
select
stu.sname,
stu.sid,
if(s1.score is NULL,0,s1.score) '语文',
if(s2.score is NULL,0,s2.score) '数学',
if(s3.score is NULL,0,s3.score) '英语',
if(round(avg(s.score),2) is NULL,0,round(avg(s.score),2)) '平均成绩'
from student stu
left join sc s on stu.sid = s.sid
left join sc s1 on s.sid = s1.sid and s1.cid = '01'
left join sc s2 on s.sid = s2.sid and s2.cid = '02'
left join sc s3 on s.sid = s3.sid and s3.cid = '03'
group by stu.sid
order by 6 desc;
mysql> select
-> stu.sname,
-> stu.sid,
-> if(s1.score is NULL,0,s1.score) '语文',
-> if(s2.score is NULL,0,s2.score) '数学',
-> if(s3.score is NULL,0,s3.score) '英语',
-> if(round(avg(s.score),2) is NULL,0,round(avg(s.score),2)) '平均成绩'
-> from student stu
-> left join sc s on stu.sid = s.sid
-> left join sc s1 on s.sid = s1.sid and s1.cid = '01'
-> left join sc s2 on s.sid = s2.sid and s2.cid = '02'
-> left join sc s3 on s.sid = s3.sid and s3.cid = '03'
-> group by stu.sid
-> order by 6 desc;
+--------+-----+--------+--------+--------+--------------+
| sname | sid | 语文 | 数学 | 英语 | 平均成绩 |
+--------+-----+--------+--------+--------+--------------+
| 郑竹 | 07 | 0.0 | 89.0 | 98.0 | 93.50 |
| 赵雷 | 01 | 80.0 | 90.0 | 99.0 | 89.67 |
| 周梅 | 05 | 76.0 | 87.0 | 0.0 | 81.50 |
| 孙风 | 03 | 80.0 | 80.0 | 80.0 | 80.00 |
| 钱电 | 02 | 70.0 | 60.0 | 80.0 | 70.00 |
| 李云 | 04 | 50.0 | 30.0 | 20.0 | 33.33 |
| 吴兰 | 06 | 31.0 | 0.0 | 34.0 | 32.50 |
| 王菊 | 08 | 0.0 | 0.0 | 0.0 | 0 |
+--------+-----+--------+--------+--------+--------------+
8 rows in set (0.00 sec)
4.18、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：>=60，中等为：70-80，优良为：80-90，优秀为：>=90
case when score then 1 else 0 end -- 总人数
case when score >= 60 then 1 else 0 end -- 及格
case when score > 70 and score <= 80 then 1 else 0 end -- 中等
case when score > 80 and score < 90 then 1 else 0 end -- 优良
case when score >= 90 then 1 else 0 end -- 优秀
select
sc.cid 课程ID,
c.cname 课程name,
max(sc.score) 最高分,
min(sc.score) 最低分,
round(avg(sc.score),2) 平均分,
round(100*(sum(case when score >= 60 then 1 else 0 end) / sum(case when score then 1 else 0 end)),2) 及格率,
round(100*(sum(case when score > 70 and score <= 80 then 1 else 0 end) / sum(case when score then 1 else 0 end)),2) 中等率,
round(100*(sum(case when score > 80 and score < 90 then 1 else 0 end) / sum(case when score then 1 else 0 end)),2) 优良率,
round(100*(sum(case when score >= 90 then 1 else 0 end) / sum(case when score then 1 else 0 end)),2) 优秀率
from sc
left join course c on sc.cid = c.cid
group by sc.cid,c.cname;
mysql> select
-> sc.cid 课程ID,
-> c.cname 课程name,
-> max(sc.score) 最高分,
-> min(sc.score) 最低分,
-> round(avg(sc.score),2) 平均分,
-> round(100*(sum(case when score >= 60 then 1 else 0 end) / sum(case when score then 1 else 0 end)),2) 及格率,
-> round(100*(sum(case when score > 70 and score <= 80 then 1 else 0 end) / sum(case when score then 1 else 0 end)),2) 中等率,
-> round(100*(sum(case when score > 80 and score < 90 then 1 else 0 end) / sum(case when score then 1 else 0 end)),2) 优良率,
-> round(100*(sum(case when score >= 90 then 1 else 0 end) / sum(case when score then 1 else 0 end)),2) 优秀率
-> from sc
-> left join course c on sc.cid = c.cid
-> group by sc.cid,c.cname;
+----------+------------+-----------+-----------+-----------+-----------+-----------+-----------+-----------+
| 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 |
+----------+------------+-----------+-----------+-----------+-----------+-----------+-----------+-----------+
| 01 | 语文 | 80.0 | 31.0 | 64.50 | 66.67 | 50.00 | 0.00 | 0.00 |
| 02 | 数学 | 90.0 | 30.0 | 72.67 | 83.33 | 16.67 | 33.33 | 16.67 |
| 03 | 英语 | 99.0 | 20.0 | 68.50 | 66.67 | 33.33 | 0.00 | 33.33 |
+----------+------------+-----------+-----------+-----------+-----------+-----------+-----------+-----------+
3 rows in set (0.00 sec)
count(1) 替换 sum(case when score then 1 else 0 end) 总人数
select
sc.cid 课程ID,
c.cname 课程name,
max(sc.score) 最高分,
min(sc.score) 最低分,
round(avg(sc.score),2) 平均分,
round(100*(sum(case when score >= 60 then 1 else 0 end) / count(1)),2) 及格率,
round(100*(sum(case when score > 70 and score <= 80 then 1 else 0 end) / count(1)),2) 中等率,
round(100*(sum(case when score > 80 and score < 90 then 1 else 0 end) / count(1)),2) 优良率,
round(100*(sum(case when score >= 90 then 1 else 0 end) / count(1)),2) 优秀率
from sc
left join course c on sc.cid = c.cid
group by sc.cid,c.cname;
mysql> select
-> sc.cid 课程ID,
-> c.cname 课程name,
-> max(sc.score) 最高分,
-> min(sc.score) 最低分,
-> round(avg(sc.score),2) 平均分,
-> round(100*(sum(case when score >= 60 then 1 else 0 end) / count(1)),2) 及格率,
-> round(100*(sum(case when score > 70 and score <= 80 then 1 else 0 end) / count(1)),2) 中等率,
-> round(100*(sum(case when score > 80 and score < 90 then 1 else 0 end) / count(1)),2) 优良率,
-> round(100*(sum(case when score >= 90 then 1 else 0 end) / count(1)),2) 优秀率
-> from sc
-> left join course c on sc.cid = c.cid
-> group by sc.cid,c.cname;
+----------+------------+-----------+-----------+-----------+-----------+-----------+-----------+-----------+
| 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 |
+----------+------------+-----------+-----------+-----------+-----------+-----------+-----------+-----------+
| 01 | 语文 | 80.0 | 31.0 | 64.50 | 66.67 | 50.00 | 0.00 | 0.00 |
| 02 | 数学 | 90.0 | 30.0 | 72.67 | 83.33 | 16.67 | 33.33 | 16.67 |
| 03 | 英语 | 99.0 | 20.0 | 68.50 | 66.67 | 33.33 | 0.00 | 33.33 |
+----------+------------+-----------+-----------+-----------+-----------+-----------+-----------+-----------+
3 rows in set (0.00 sec)
4.19、按各科成绩进行排序，并显示排名
select
s1.sid,
s1.cid,
s1.score,
(select count(distinct score) from sc where cid = s1.cid and score >s1.score)+1 AS 排名
from sc s1
order by s1.cid,4;
mysql> select
-> s1.sid,
-> s1.cid,
-> s1.score,
-> (select count(distinct score) from sc where cid = s1.cid and score >s1.score)+1 AS 排名
-> from sc s1
-> order by s1.cid,4;
+-----+-----+-------+--------+
| sid | cid | score | 排名 |
+-----+-----+-------+--------+
| 01 | 01 | 80.0 | 1 |
| 03 | 01 | 80.0 | 1 |
| 05 | 01 | 76.0 | 2 |
| 02 | 01 | 70.0 | 3 |
| 04 | 01 | 50.0 | 4 |
| 06 | 01 | 31.0 | 5 |
| 01 | 02 | 90.0 | 1 |
| 07 | 02 | 89.0 | 2 |
| 05 | 02 | 87.0 | 3 |
| 03 | 02 | 80.0 | 4 |
| 02 | 02 | 60.0 | 5 |
| 04 | 02 | 30.0 | 6 |
| 01 | 03 | 99.0 | 1 |
| 07 | 03 | 98.0 | 2 |
| 02 | 03 | 80.0 | 3 |
| 03 | 03 | 80.0 | 3 |
| 06 | 03 | 34.0 | 4 |
| 04 | 03 | 20.0 | 5 |
+-----+-----+-------+--------+
18 rows in set (0.00 sec)
select
stu.sname '学生姓名',
c.cname '课程名',
s1.score '分数',
(select count(distinct score) from sc where cid = s1.cid and score >s1.score)+1 AS 排名
from sc s1
join student stu on s1.sid = stu.sid
join course c on s1.cid = c.cid
order by s1.cid,4;
mysql> select
-> stu.sname '学生姓名',
-> c.cname '课程名',
-> s1.score '分数',
-> (select count(distinct score) from sc where cid = s1.cid and score >s1.score)+1 AS 排名
-> from sc s1
-> join student stu on s1.sid = stu.sid
-> join course c on s1.cid = c.cid
-> order by s1.cid,4;
+--------------+-----------+--------+--------+
| 学生姓名 | 课程名 | 分数 | 排名 |
+--------------+-----------+--------+--------+
| 赵雷 | 语文 | 80.0 | 1 |
| 孙风 | 语文 | 80.0 | 1 |
| 周梅 | 语文 | 76.0 | 2 |
| 钱电 | 语文 | 70.0 | 3 |
| 李云 | 语文 | 50.0 | 4 |
| 吴兰 | 语文 | 31.0 | 5 |
| 赵雷 | 数学 | 90.0 | 1 |
| 郑竹 | 数学 | 89.0 | 2 |
| 周梅 | 数学 | 87.0 | 3 |
| 孙风 | 数学 | 80.0 | 4 |
| 钱电 | 数学 | 60.0 | 5 |
| 李云 | 数学 | 30.0 | 6 |
| 赵雷 | 英语 | 99.0 | 1 |
| 郑竹 | 英语 | 98.0 | 2 |
| 孙风 | 英语 | 80.0 | 3 |
| 钱电 | 英语 | 80.0 | 3 |
| 吴兰 | 英语 | 34.0 | 4 |
| 李云 | 英语 | 20.0 | 5 |
+--------------+-----------+--------+--------+
18 rows in set (0.01 sec)
4.20、查询学生的总成绩并进行排名
select
stu.sname '学生姓名',
sum(score) '总成绩'
from sc
inner join student stu on sc.sid = stu.sid
group by sc.sid
order by 2 asc;
mysql> select
-> stu.sname '学生姓名',
-> sum(score) '总成绩'
-> from sc
-> inner join student stu on sc.sid = stu.sid
-> group by sc.sid
-> order by 2 asc;
+--------------+-----------+
| 学生姓名 | 总成绩 |
+--------------+-----------+
| 吴兰 | 65.0 |
| 李云 | 100.0 |
| 周梅 | 163.0 |
| 郑竹 | 187.0 |
| 钱电 | 210.0 |
| 孙风 | 240.0 |
| 赵雷 | 269.0 |
+--------------+-----------+
7 rows in set (0.00 sec)
select sid,sum(score) sscore from sc group by sid;
select
stu.sname '学生姓名',
t1.sscore '总成绩',
(select count(distinct t2.sscore)
from (select sid,sum(score) sscore from sc group by sid) t2
where t2.sscore > t1.sscore
)+1 '排名'
from student stu,(select sid,sum(score) sscore from sc group by sid) t1
where stu.sid = t1.sid
order by 3;
mysql> select
-> stu.sname '学生姓名',
-> t1.sscore '总成绩',
-> (select count(distinct t2.sscore)
-> from (select sid,sum(score) sscore from sc group by sid) t2
-> where t2.sscore > t1.sscore
-> )+1 '排名'
-> from student stu,(select sid,sum(score) sscore from sc group by sid) t1
-> where stu.sid = t1.sid
-> order by 3;
+--------------+-----------+--------+
| 学生姓名 | 总成绩 | 排名 |
+--------------+-----------+--------+
| 赵雷 | 269.0 | 1 |
| 孙风 | 240.0 | 2 |
| 钱电 | 210.0 | 3 |
| 郑竹 | 187.0 | 4 |
| 周梅 | 163.0 | 5 |
| 李云 | 100.0 | 6 |
| 吴兰 | 65.0 | 7 |
+--------------+-----------+--------+
7 rows in set (0.00 sec)
4.21、查询不同老师所教不同课程平均分从高到低显示
select c.cid,c.cname,t.tname
from course c
join teacher t on c.tid = t.tid;
mysql> select c.cid,c.cname,t.tname
-> from course c
-> join teacher t on c.tid = t.tid;
+-----+--------+--------+
| cid | cname | tname |
+-----+--------+--------+
| 02 | 数学 | 张三 |
| 01 | 语文 | 李四 |
| 03 | 英语 | 王五 |
+-----+--------+--------+
3 rows in set (0.00 sec)
select cid,avg(score) from sc group by cid;
mysql> select cid,avg(score) from sc group by cid;
+-----+------------+
| cid | avg(score) |
+-----+------------+
| 01 | 64.50000 |
| 02 | 72.66667 |
| 03 | 68.50000 |
+-----+------------+
3 rows in set (0.00 sec)
select c.cid '课程ID',c.cname '课程名',t.tname '教师名',score.avgscore '课程均分'
from course c
join teacher t on c.tid = t.tid
join (select cid,avg(score) avgscore from sc group by cid) score on c.cid = score.cid
order by 4 desc;
mysql> select c.cid '课程ID',c.cname '课程名',t.tname '教师名',score.avgscore '课程均分'
-> from course c
-> join teacher t on c.tid = t.tid
-> join (select cid,avg(score) avgscore from sc group by cid) score on c.cid = score.cid
-> order by 4 desc;
+----------+-----------+-----------+--------------+
| 课程ID | 课程名 | 教师名 | 课程均分 |
+----------+-----------+-----------+--------------+
| 02 | 数学 | 张三 | 72.66667 |
| 03 | 英语 | 王五 | 68.50000 |
| 01 | 语文 | 李四 | 64.50000 |
+----------+-----------+-----------+--------------+
3 rows in set (0.00 sec)
select c.cid '课程ID',c.cname '课程名',t.tname '教师名',round(avg(score),2) '课程均分'
from course c
left join teacher t on c.tid = t.tid
left join sc on c.cid = sc.cid
group by c.cid
order by 4 desc;
mysql> select c.cid '课程ID',c.cname '课程名',t.tname '教师名',round(avg(score),2) '课程均分'
-> from course c
-> left join teacher t on c.tid = t.tid
-> left join sc on c.cid = sc.cid
-> group by c.cid
-> order by 4 desc;
+----------+-----------+-----------+--------------+
| 课程ID | 课程名 | 教师名 | 课程均分 |
+----------+-----------+-----------+--------------+
| 02 | 数学 | 张三 | 72.67 |
| 03 | 英语 | 王五 | 68.50 |
| 01 | 语文 | 李四 | 64.50 |
+----------+-----------+-----------+--------------+
3 rows in set (0.00 sec)
4.22、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;
select
s1.*,
(select count(distinct score) from sc where cid = s1.cid and score > s1.score)+1 '排名'
from sc s1;
mysql> select
-> s1.*,
-> (select count(distinct score) from sc where cid = s1.cid and score > s1.score)+1 '排名'
-> from sc s1;
+-----+-----+-------+--------+
| sid | cid | score | 排名 |
+-----+-----+-------+--------+
| 01 | 01 | 80.0 | 1 |
| 01 | 02 | 90.0 | 1 |
| 01 | 03 | 99.0 | 1 |
| 02 | 01 | 70.0 | 3 |
| 02 | 02 | 60.0 | 5 |
| 02 | 03 | 80.0 | 3 |
| 03 | 01 | 80.0 | 1 |
| 03 | 02 | 80.0 | 4 |
| 03 | 03 | 80.0 | 3 |
| 04 | 01 | 50.0 | 4 |
| 04 | 02 | 30.0 | 6 |
| 04 | 03 | 20.0 | 5 |
| 05 | 01 | 76.0 | 2 |
| 05 | 02 | 87.0 | 3 |
| 06 | 01 | 31.0 | 5 |
| 06 | 03 | 34.0 | 4 |
| 07 | 02 | 89.0 | 2 |
| 07 | 03 | 98.0 | 2 |
+-----+-----+-------+--------+
18 rows in set (0.00 sec)
select
stu.sname '学生名字',
c.cname '课程名',
s1.score '分数',
(select count(distinct score) from sc where cid = s1.cid and score > s1.score)+1 rank
from sc s1
inner join student stu on s1.sid = stu.sid
inner join course c on s1.cid = c.cid
having rank between 2 and 3
order by 4 desc;
mysql> select
-> stu.sname '学生名字',
-> c.cname '课程名',
-> s1.score '分数',
-> (select count(distinct score) from sc where cid = s1.cid and score > s1.score)+1 rank
-> from sc s1
-> inner join student stu on s1.sid = stu.sid
-> inner join course c on s1.cid = c.cid
-> having rank between 2 and 3
-> order by 4 desc;
+--------------+-----------+--------+------+
| 学生名字 | 课程名 | 分数 | rank |
+--------------+-----------+--------+------+
| 钱电 | 英语 | 80.0 | 3 |
| 钱电 | 语文 | 70.0 | 3 |
| 孙风 | 英语 | 80.0 | 3 |
| 周梅 | 数学 | 87.0 | 3 |
| 郑竹 | 数学 | 89.0 | 2 |
| 周梅 | 语文 | 76.0 | 2 |
| 郑竹 | 英语 | 98.0 | 2 |
+--------------+-----------+--------+------+
7 rows in set (0.01 sec)
4.23、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
sc.cid '课程编号',
sum(case when score >= 0 and score < 60 then 1 else 0 end) '0-60人数',
round(100 * (sum(case when score >= 0 and score < 60 then 1 else 0 end) / count(*) ),2) '0-60占比'
from sc
group by sc.cid; -- 分课程统计
mysql> select
-> sc.cid '课程编号',
-> sum(case when score >= 0 and score < 60 then 1 else 0 end) '0-60人数',
-> round(100 * (sum(case when score >= 0 and score < 60 then 1 else 0 end) / count(*) ),2) '0-60占比'
-> from sc
-> group by sc.cid; -- 分课程统计
+--------------+------------+------------+
| 课程编号 | 0-60人数 | 0-60占比 |
+--------------+------------+------------+
| 01 | 2 | 33.33 |
| 02 | 1 | 16.67 |
| 03 | 2 | 33.33 |
+--------------+------------+------------+
3 rows in set (0.00 sec)
select
sc.cid '课程编号',
c.cname '科目',
count(*) '课程人数',
sum(case when score >= 85 then 1 else 0 end) '85-100人数',
round(100 * (sum(case when score > 85 then 1 else 0 end) / count(*) ),2) '85-100占比',
sum(case when score < 85 and score >= 70 then 1 else 0 end) '70-85人数',
round(100 * (sum(case when score < 85 and score >= 70 then 1 else 0 end) / count(*) ),2) '70-85占比',
sum(case when score < 70 and score >= 60 then 1 else 0 end) '60-70人数',
round(100 * (sum(case when score < 70 and score >= 60 then 1 else 0 end) / count(*) ),2) '60-70占比',
sum(case when score >= 0 and score < 60 then 1 else 0 end) '0-60人数',
round(100 * (sum(case when score >= 0 and score < 60 then 1 else 0 end) / count(*) ),2) '0-60占比'
from sc
left join course c on sc.cid = c.cid
group by sc.cid -- 分课程统计
order by sc.cid;
mysql> select
-> sc.cid '课程编号',
-> c.cname '科目',
-> count(*) '课程人数',
-> sum(case when score >= 85 then 1 else 0 end) '85-100人数',
-> round(100 * (sum(case when score > 85 then 1 else 0 end) / count(*) ),2) '85-100占比',
-> sum(case when score < 85 and score >= 70 then 1 else 0 end) '70-85人数',
-> round(100 * (sum(case when score < 85 and score >= 70 then 1 else 0 end) / count(*) ),2) '70-85占比',
-> sum(case when score < 70 and score >= 60 then 1 else 0 end) '60-70人数',
-> round(100 * (sum(case when score < 70 and score >= 60 then 1 else 0 end) / count(*) ),2) '60-70占比',
-> sum(case when score >= 0 and score < 60 then 1 else 0 end) '0-60人数',
-> round(100 * (sum(case when score >= 0 and score < 60 then 1 else 0 end) / count(*) ),2) '0-60占比'
-> from sc
-> left join course c on sc.cid = c.cid
-> group by sc.cid -- 分课程统计
-> order by sc.cid;
+--------------+--------+--------------+--------------+--------------+-------------+-------------+-------------+-------------+------------+------------+
| 课程编号 | 科目 | 课程人数 | 85-100人数 | 85-100占比 | 70-85人数 | 70-85占比 | 60-70人数 | 60-70占比 | 0-60人数 | 0-60占比 |
+--------------+--------+--------------+--------------+--------------+-------------+-------------+-------------+-------------+------------+------------+
| 01 | 语文 | 6 | 0 | 0.00 | 4 | 66.67 | 0 | 0.00 | 2 | 33.33 |
| 02 | 数学 | 6 | 3 | 50.00 | 1 | 16.67 | 1 | 16.67 | 1 | 16.67 |
| 03 | 英语 | 6 | 2 | 33.33 | 2 | 33.33 | 0 | 0.00 | 2 | 33.33 |
+--------------+--------+--------------+--------------+--------------+-------------+-------------+-------------+-------------+------------+------------+
3 rows in set (0.01 sec)
4.24、查询学生平均成绩及其名次
select
sc.sid,
avg(score) '平均成绩'
from sc
group by sc.sid
mysql> select
-> sc.sid,
-> avg(score) '平均成绩'
-> from sc
-> group by sc.sid;
+-----+--------------+
| sid | 平均成绩 |
+-----+--------------+
| 01 | 89.66667 |
| 02 | 70.00000 |
| 03 | 80.00000 |
| 04 | 33.33333 |
| 05 | 81.50000 |
| 06 | 32.50000 |
| 07 | 93.50000 |
+-----+--------------+
7 rows in set (0.00 sec)
-- 查询平均成绩并去重
select distinct avg(score) avg_score from sc group by sid;
mysql> select distinct avg(score) avg_score from sc group by sid;
+-----------+
| avg_score |
+-----------+
| 89.66667 |
| 70.00000 |
| 80.00000 |
| 33.33333 |
| 81.50000 |
| 32.50000 |
| 93.50000 |
+-----------+
7 rows in set (0.00 sec)
select
stu.sid,
t.avg_score '平均成绩',
(select count(*)
from (select distinct avg(score) avg_score from sc group by sid) t2 -- 查询平均成绩并去重
where t2.avg_score > t.avg_score
)+1 '排名'
from student stu,(select avg(score) avg_score,sid from sc group by sid) t
where stu.sid = t.sid
group by stu.sid
order by 3;
mysql> select
-> stu.sid,
-> t.avg_score '平均成绩',
-> (select count(*)
-> from (select distinct avg(score) avg_score from sc group by sid) t2 -- 查询平均成绩并去重
-> where t2.avg_score > t.avg_score
-> )+1 '排名'
-> from student stu,(select avg(score) avg_score,sid from sc group by sid) t
-> where stu.sid = t.sid
-> group by stu.sid
-> order by 3;
+-----+--------------+--------+
| sid | 平均成绩 | 排名 |
+-----+--------------+--------+
| 07 | 93.50000 | 1 |
| 01 | 89.66667 | 2 |
| 05 | 81.50000 | 3 |
| 03 | 80.00000 | 4 |
| 02 | 70.00000 | 5 |
| 04 | 33.33333 | 6 |
| 06 | 32.50000 | 7 |
+-----+--------------+--------+
7 rows in set (0.00 sec)
select
stu.sid,
t.avg_score '平均成绩',
(select count(*)
from (select distinct avg(score) avg_score from sc group by sid) t2 -- 查询平均成绩并去重
where t2.avg_score > t.avg_score
)+1 '排名'
from student stu,(select avg(score) avg_score,sid from sc group by sid) t
where stu.sid = t.sid
group by stu.sid;
4.24.1、MySql中@符号的使用【经典】
@符号的作用：@后接变量名，用以定义一个变量，该变量的有效期为语句级，即再一次执行中始终有效
-- 由于通常情况下=被认为是等于比较运算符，因此赋值运算符一般使用:=
SELECT @lt:=1, @lt:=@lt+1, @lt:=@lt+1;
mysql> SELECT @lt:=1, @lt:=@lt+1, @lt:=@lt+1;
+--------+------------+------------+
| @lt:=1 | @lt:=@lt+1 | @lt:=@lt+1 |
+--------+------------+------------+
| 1 | 2 | 3 |
+--------+------------+------------+
1 row in set (0.00 sec)
select
s.sid, -- 学号
@i:=@i+1 as '不保留空缺排名', -- 直接i的自加
@k:=(case when @avgscore=s.avg_score then @k else @i end) as '保留空缺排名',
@avgscore:=avg_score as '平均分' -- 表s中的值
from (select sid,round(avg(score), 2) as avg_score from sc
group by sid
order by 2 desc) s -- 表s：平均成绩的排序和学号
,(select @avgscore:=0, @i:=0, @k:=0) b; -- 表b：通过变量设置初始值
mysql> select
-> s.sid, -- 学号
-> @i:=@i+1 as '不保留空缺排名', -- 直接i的自加
-> @k:=(case when @avgscore=s.avg_score then @k else @i end) as '保留空缺排名',
-> @avgscore:=avg_score as '平均分' -- 表s中的值
->
-> from (select sid,round(avg(score), 2) as avg_score from sc
-> group by sid
-> order by 2 desc) s -- 表s：平均成绩的排序和学号
-> ,(select @avgscore:=0, @i:=0, @k:=0) b; -- 表b：通过变量设置初始值
+-----+-----------------------+--------------------+-----------+
| sid | 不保留空缺排名 | 保留空缺排名 | 平均分 |
+-----+-----------------------+--------------------+-----------+
| 07 | 1 | 1 | 93.50 |
| 01 | 2 | 2 | 89.67 |
| 05 | 3 | 3 | 81.50 |
| 03 | 4 | 4 | 80.00 |
| 02 | 5 | 5 | 70.00 |
| 04 | 6 | 6 | 33.33 |
| 06 | 7 | 7 | 32.50 |
+-----+-----------------------+--------------------+-----------+
7 rows in set (0.00 sec)
4.25、查询各科成绩前三名的记录【经典】
先看
select *
from sc s1
inner join sc s2 on s1.cid = s2.cid and s1.score <= s2.score; -- 将分数表sc自连接，通过课程id对应起来，每个分数表s2的成绩最大
然后是
select s1.*,count(s2.score)
from sc s1
inner join sc s2 on s1.cid = s2.cid and s1.score <= s2.score
group by s1.sid,s1.cid,s1.score;
然后是
select s1.*,count(distinct s2.score)
from sc s1
inner join sc s2 on s1.cid = s2.cid and s1.score <= s2.score
group by s1.sid,s1.cid,s1.score;
最后是
select s1.*,count(distinct s2.score) rank
from sc s1
inner join sc s2 on s1.cid = s2.cid and s1.score <= s2.score
group by s1.sid,s1.cid,s1.score
having count(distinct s2.score) <=3
order by s1.cid,rank;
mysql> select s1.*,count(distinct s2.score) rank
-> from sc s1
-> inner join sc s2 on s1.cid = s2.cid and s1.score <= s2.score
-> group by s1.sid,s1.cid,s1.score
-> having count(distinct s2.score) <=3
-> order by s1.cid,rank;
+-----+-----+-------+------+
| sid | cid | score | rank |
+-----+-----+-------+------+
| 03 | 01 | 80.0 | 1 |
| 01 | 01 | 80.0 | 1 |
| 05 | 01 | 76.0 | 2 |
| 02 | 01 | 70.0 | 3 |
| 01 | 02 | 90.0 | 1 |
| 07 | 02 | 89.0 | 2 |
| 05 | 02 | 87.0 | 3 |
| 01 | 03 | 99.0 | 1 |
| 07 | 03 | 98.0 | 2 |
| 02 | 03 | 80.0 | 3 |
| 03 | 03 | 80.0 | 3 |
+-----+-----+-------+------+
11 rows in set (0.00 sec)
4.26、查询每门课程被选修的学生数
select
c.cid,
c.cname,
count(sc.cid)
from course c
inner join sc on c.cid = sc.cid
group by c.cid;
mysql> select
-> c.cid,
-> c.cname,
-> count(sc.cid)
-> from course c
-> inner join sc on c.cid = sc.cid
-> group by c.cid;
+-----+--------+---------------+
| cid | cname | count(sc.cid) |
+-----+--------+---------------+
| 01 | 语文 | 6 |
| 02 | 数学 | 6 |
| 03 | 英语 | 6 |
+-----+--------+---------------+
3 rows in set (0.00 sec)
4.27、查询出只有两门课程的全部学生的学号和姓名
select
stu.sid '学号',
stu.sname '姓名'
from student stu
inner join sc on stu.sid = sc.sid
group by stu.sid
having count(sc.sid) = 2;
mysql> select
-> stu.sid '学号',
-> stu.sname '姓名'
-> from student stu
-> inner join sc on stu.sid = sc.sid
-> group by stu.sid
-> having count(sc.sid) = 2;
+--------+--------+
| 学号 | 姓名 |
+--------+--------+
| 05 | 周梅 |
| 06 | 吴兰 |
| 07 | 郑竹 |
+--------+--------+
3 rows in set (0.00 sec)
4.28、查询男生、女生人数
select
ssex '性别',
count(ssex) '人数'
from student
group by ssex;
mysql> select
-> ssex '性别',
-> count(ssex) '人数'
-> from student
-> group by ssex;
+--------+--------+
| 性别 | 人数 |
+--------+--------+
| 女 | 4 |
| 男 | 4 |
+--------+--------+
2 rows in set (0.00 sec)
select
count(case when ssex = '男' then 1 else 0 end) '男',
count(case when ssex = '女' then 1 else 0 end) '女'
from student;
mysql> select
-> count(case when ssex = '男' then 1 else 0 end) '男',
-> count(case when ssex = '女' then 1 else 0 end) '女'
-> from student;
+-----+-----+
| 男 | 女 |
+-----+-----+
| 8 | 8 |
+-----+-----+
1 row in set (0.00 sec)
select count(ssex='女') '女',count(ssex='男') '男' from student;
mysql> select count(ssex='女') '女',count(ssex='男') '男' from student;
+-----+-----+
| 女 | 男 |
+-----+-----+
| 8 | 8 |
+-----+-----+
1 row in set (0.00 sec)
4.29、查询名字中含有"风"字的学生信息
select
student.*
from student
where sname like '%风%';
mysql> select
-> student.*
-> from student
-> where sname like '%风%';
+-----+--------+---------------------+------+
| sid | sname | sage | ssex |
+-----+--------+---------------------+------+
| 03 | 孙风 | 1990-05-20 00:00:00 | 男 |
+-----+--------+---------------------+------+
1 row in set (0.00 sec)
4.30、查询同名同性学生名单，并统计同名人数
INSERT INTO student VALUES('09' , '赵雷' , '2013-05-21' , '男'),('10' , '王菊' , '1314-12-25' , '女');
select
s1.sname,
s1.ssex,
count(*)
from student s1
inner join student s2 on s1.sid <> s2.sid and s1.sname = s2.sname and s1.ssex = s2.ssex
group by s1.sname,s1.ssex;
mysql> INSERT INTO student VALUES('09' , '赵雷' , '2013-05-21' , '男'),('10' , '王菊' , '1314-12-25' , '女');
Query OK, 2 rows affected (0.01 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> select
-> s1.sname,
-> s1.ssex,
-> count(*)
-> from student s1
-> inner join student s2 on s1.sid <> s2.sid and s1.sname = s2.sname and s1.ssex = s2.ssex
-> group by s1.sname,s1.ssex;
+--------+------+----------+
| sname | ssex | count(*) |
+--------+------+----------+
| 王菊 | 女 | 2 |
| 赵雷 | 男 | 2 |
+--------+------+----------+
2 rows in set (0.00 sec)
mysql> delete from student where sid in ('09','10');
Query OK, 2 rows affected (0.00 sec)
delete from student where sid in ('09','10');
4.31、查询1990年出生的学生名单
select
student.*
from student
where year(sage) = 1990;
mysql> select
-> student.*
-> from student
-> where year(sage) = 1990;
+-----+--------+---------------------+------+
| sid | sname | sage | ssex |
+-----+--------+---------------------+------+
| 01 | 赵雷 | 1990-01-01 00:00:00 | 男 |
| 02 | 钱电 | 1990-12-21 00:00:00 | 男 |
| 03 | 孙风 | 1990-05-20 00:00:00 | 男 |
| 04 | 李云 | 1990-08-06 00:00:00 | 男 |
| 08 | 王菊 | 1990-01-20 00:00:00 | 女 |
+-----+--------+---------------------+------+
5 rows in set (0.00 sec)
select
student.*
from student
where sage like '1990%';
mysql> select
-> student.*
-> from student
-> where sage like '1990%';
+-----+--------+---------------------+------+
| sid | sname | sage | ssex |
+-----+--------+---------------------+------+
| 01 | 赵雷 | 1990-01-01 00:00:00 | 男 |
| 02 | 钱电 | 1990-12-21 00:00:00 | 男 |
| 03 | 孙风 | 1990-05-20 00:00:00 | 男 |
| 04 | 李云 | 1990-08-06 00:00:00 | 男 |
| 08 | 王菊 | 1990-01-20 00:00:00 | 女 |
+-----+--------+---------------------+------+
5 rows in set, 1 warning (0.00 sec)
4.32、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
sc.cid '课程编号',
avg(score) '平均成绩'
from sc
group by cid
order by 2 desc,1 asc;
mysql> select
-> sc.cid '课程编号',
-> avg(score) '平均成绩'
-> from sc
-> group by cid
-> order by 2 desc,1 asc;
+--------------+--------------+
| 课程编号 | 平均成绩 |
+--------------+--------------+
| 02 | 72.66667 |
| 03 | 68.50000 |
| 01 | 64.50000 |
+--------------+--------------+
3 rows in set (0.00 sec)
4.33、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
stu.sid '学号',
stu.sname '姓名',
avg(score) '平均成绩'
from sc
join student stu on sc.sid = stu.sid
group by sc.sid
having avg(score) >= 85;
mysql> select
-> stu.sid '学号',
-> stu.sname '姓名',
-> avg(score) '平均成绩'
-> from sc
-> join student stu on sc.sid = stu.sid
-> group by sc.sid
-> having avg(score) >= 85;
+--------+--------+--------------+
| 学号 | 姓名 | 平均成绩 |
+--------+--------+--------------+
| 01 | 赵雷 | 89.66667 |
| 07 | 郑竹 | 93.50000 |
+--------+--------+--------------+
2 rows in set (0.00 sec)
4.34、查询课程名称为"数学"，且分数低于60的学生姓名和分数
select
stu.sname '学生姓名',
sc.score '分数'
from sc
inner join student stu on sc.sid = stu.sid
inner join course c on sc.cid = c.cid and c.cname = '数学'
where sc.score < 60;
mysql> select
-> stu.sname '学生姓名',
-> sc.score '分数'
-> from sc
-> inner join student stu on sc.sid = stu.sid
-> inner join course c on sc.cid = c.cid and c.cname = '数学'
-> where sc.score < 60;
+--------------+--------+
| 学生姓名 | 分数 |
+--------------+--------+
| 李云 | 30.0 |
+--------------+--------+
1 row in set (0.00 sec)
4.35、查询所有学生的课程及分数情况；
select
stu.sid,
stu.sname,
sum(case when sc.cid = '01' then sc.score else 0 end) '语文',
sum(case when sc.cid = '02' then sc.score else 0 end) '数学',
sum(case when sc.cid = '03' then sc.score else 0 end) '英语',
sum(sc.score)
from student stu
left join sc on stu.sid = sc.sid
group by stu.sid,stu.sname;
mysql> select
-> stu.sid,
-> stu.sname,
-> sum(case when sc.cid = '01' then sc.score else 0 end) '语文',
-> sum(case when sc.cid = '02' then sc.score else 0 end) '数学',
-> sum(case when sc.cid = '03' then sc.score else 0 end) '英语',
-> sum(sc.score)
-> from student stu
-> left join sc on stu.sid = sc.sid
-> group by stu.sid,stu.sname;
+-----+--------+--------+--------+--------+---------------+
| sid | sname | 语文 | 数学 | 英语 | sum(sc.score) |
+-----+--------+--------+--------+--------+---------------+
| 01 | 赵雷 | 80.0 | 90.0 | 99.0 | 269.0 |
| 02 | 钱电 | 70.0 | 60.0 | 80.0 | 210.0 |
| 03 | 孙风 | 80.0 | 80.0 | 80.0 | 240.0 |
| 04 | 李云 | 50.0 | 30.0 | 20.0 | 100.0 |
| 05 | 周梅 | 76.0 | 87.0 | 0.0 | 163.0 |
| 06 | 吴兰 | 31.0 | 0.0 | 34.0 | 65.0 |
| 07 | 郑竹 | 0.0 | 89.0 | 98.0 | 187.0 |
| 08 | 王菊 | 0.0 | 0.0 | 0.0 | NULL |
+-----+--------+--------+--------+--------+---------------+
8 rows in set (0.00 sec)
select
stu.sid,
stu.sname,
sum(case c.cname when '语文' then sc.score else 0 end) '语文',
sum(case c.cname when '数学' then sc.score else 0 end) '数学',
sum(case c.cname when '英语' then sc.score else 0 end) '英语',
sum(sc.score)
from student stu
left join sc on stu.sid = sc.sid
left join course c on sc.cid = c.cid
group by stu.sid;
mysql> select
-> stu.sid,
-> stu.sname,
-> sum(case c.cname when '语文' then sc.score else 0 end) '语文',
-> sum(case c.cname when '数学' then sc.score else 0 end) '数学',
-> sum(case c.cname when '英语' then sc.score else 0 end) '英语',
-> sum(sc.score)
-> from student stu
-> left join sc on stu.sid = sc.sid
-> left join course c on sc.cid = c.cid
-> group by stu.sid;
+-----+--------+--------+--------+--------+---------------+
| sid | sname | 语文 | 数学 | 英语 | sum(sc.score) |
+-----+--------+--------+--------+--------+---------------+
| 01 | 赵雷 | 80.0 | 90.0 | 99.0 | 269.0 |
| 02 | 钱电 | 70.0 | 60.0 | 80.0 | 210.0 |
| 03 | 孙风 | 80.0 | 80.0 | 80.0 | 240.0 |
| 04 | 李云 | 50.0 | 30.0 | 20.0 | 100.0 |
| 05 | 周梅 | 76.0 | 87.0 | 0.0 | 163.0 |
| 06 | 吴兰 | 31.0 | 0.0 | 34.0 | 65.0 |
| 07 | 郑竹 | 0.0 | 89.0 | 98.0 | 187.0 |
| 08 | 王菊 | 0.0 | 0.0 | 0.0 | NULL |
+-----+--------+--------+--------+--------+---------------+
8 rows in set (0.00 sec)
4.36、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
stu.sname,
c.cname,
sc.score
from sc
join student stu on sc.sid = stu.sid
join course c on sc.cid = c.cid
having score > 70;
mysql> select
-> stu.sname,
-> c.cname,
-> sc.score
-> from sc
-> join student stu on sc.sid = stu.sid
-> join course c on sc.cid = c.cid
-> having score > 70;
+--------+--------+-------+
| sname | cname | score |
+--------+--------+-------+
| 赵雷 | 语文 | 80.0 |
| 赵雷 | 数学 | 90.0 |
| 赵雷 | 英语 | 99.0 |
| 钱电 | 英语 | 80.0 |
| 孙风 | 语文 | 80.0 |
| 孙风 | 数学 | 80.0 |
| 孙风 | 英语 | 80.0 |
| 周梅 | 语文 | 76.0 |
| 周梅 | 数学 | 87.0 |
| 郑竹 | 数学 | 89.0 |
| 郑竹 | 英语 | 98.0 |
+--------+--------+-------+
11 rows in set (0.00 sec)
4.37、查询不及格的课程
select
sc.sid,
c.cname,
sc.score
from sc
join course c on sc.cid = c.cid
where sc.score < 60;
mysql> select
-> sc.sid,
-> c.cname,
-> sc.score
-> from sc
-> join course c on sc.cid = c.cid
-> where sc.score < 60;
+-----+--------+-------+
| sid | cname | score |
+-----+--------+-------+
| 04 | 语文 | 50.0 |
| 04 | 数学 | 30.0 |
| 04 | 英语 | 20.0 |
| 06 | 语文 | 31.0 |
| 06 | 英语 | 34.0 |
+-----+--------+-------+
5 rows in set (0.00 sec)
4.38、查询课程编号为01且课程成绩在80分及以上的学生的学号和姓名
select
stu.sid,
stu.sname,
sc.score
from sc
join student stu on sc.sid = stu.sid
where sc.score >= 80 and sc.cid = '01';
mysql> select
-> stu.sid,
-> stu.sname,
-> sc.score
-> from sc
-> join student stu on sc.sid = stu.sid
-> where sc.score >= 80 and sc.cid = '01';
+-----+--------+-------+
| sid | sname | score |
+-----+--------+-------+
| 01 | 赵雷 | 80.0 |
| 03 | 孙风 | 80.0 |
+-----+--------+-------+
2 rows in set (0.00 sec)
4.39、求每门课程的学生人数
select
c.cname '课程名',
count(*) '学生人数'
from course c
join sc on c.cid = sc.cid
group by c.cid;
mysql> select
-> c.cname '课程名',
-> count(*) '学生人数'
-> from course c
-> join sc on c.cid = sc.cid
-> group by c.cid;
+-----------+--------------+
| 课程名 | 学生人数 |
+-----------+--------------+
| 语文 | 6 |
| 数学 | 6 |
| 英语 | 6 |
+-----------+--------------+
3 rows in set (0.01 sec)
4.40、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
stu.sid,
stu.sname,
sc.score,
c.cname,
t.tname
from sc
left join course c on c.cid = sc.cid
left join teacher t on c.tid = t.tid
left join student stu on sc.sid = stu.sid
where t.tname = '张三';
mysql> select
-> stu.sid,
-> stu.sname,
-> sc.score,
-> c.cname,
-> t.tname
-> from sc
-> left join course c on c.cid = sc.cid
-> left join teacher t on c.tid = t.tid
-> left join student stu on sc.sid = stu.sid
-> where t.tname = '张三';
+------+--------+-------+--------+--------+
| sid | sname | score | cname | tname |
+------+--------+-------+--------+--------+
| 01 | 赵雷 | 90.0 | 数学 | 张三 |
| 02 | 钱电 | 60.0 | 数学 | 张三 |
| 03 | 孙风 | 80.0 | 数学 | 张三 |
| 04 | 李云 | 30.0 | 数学 | 张三 |
| 05 | 周梅 | 87.0 | 数学 | 张三 |
| 07 | 郑竹 | 89.0 | 数学 | 张三 |
+------+--------+-------+--------+--------+
6 rows in set (0.00 sec)
select
stu.sid,
stu.sname,
max(sc.score),
c.cname,
t.tname
from sc
left join course c on c.cid = sc.cid
left join teacher t on c.tid = t.tid
left join student stu on sc.sid = stu.sid
where t.tname = '张三';
mysql> select
-> stu.sid,
-> stu.sname,
-> max(sc.score),
-> c.cname,
-> t.tname
-> from sc
-> left join course c on c.cid = sc.cid
-> left join teacher t on c.tid = t.tid
-> left join student stu on sc.sid = stu.sid
-> where t.tname = '张三';
+------+--------+---------------+--------+--------+
| sid | sname | max(sc.score) | cname | tname |
+------+--------+---------------+--------+--------+
| 01 | 赵雷 | 90.0 | 数学 | 张三 |
+------+--------+---------------+--------+--------+
1 row in set (0.00 sec)
4.41、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
distinct s1.sid,
s1.cid,
s1.score
from sc s1
join sc s2 on s1.score = s2.score and s1.cid != s2.cid and s1.sid != s2.sid;
mysql> select
-> distinct s1.sid,
-> s1.cid,
-> s1.score
-> from sc s1
-> join sc s2 on s1.score = s2.score and s1.cid != s2.cid and s1.sid != s2.sid;
+-----+-----+-------+
| sid | cid | score |
+-----+-----+-------+
| 02 | 03 | 80.0 |
| 03 | 02 | 80.0 |
| 03 | 03 | 80.0 |
| 01 | 01 | 80.0 |
| 03 | 01 | 80.0 |
+-----+-----+-------+
5 rows in set (0.00 sec)
-- 查询成绩相同的分数
select score from sc group by score having count(1)>1;
select
sc.sid,
sc.cid,
sc.score
from sc
where sc.score in (select score from sc group by score having count(1)>1);
mysql> select
-> sc.sid,
-> sc.cid,
-> sc.score
-> from sc
-> where sc.score in (select score from sc group by score having count(1)>1);
+-----+-----+-------+
| sid | cid | score |
+-----+-----+-------+
| 01 | 01 | 80.0 |
| 02 | 03 | 80.0 |
| 03 | 01 | 80.0 |
| 03 | 02 | 80.0 |
| 03 | 03 | 80.0 |
+-----+-----+-------+
5 rows in set (0.00 sec)
4.42、查询每门功课成绩最好的前两名【经典】
select
s1.*,
count(distinct(s2.score)) rank
from sc s1
join sc s2 on s1.cid = s2.cid and s1.score <= s2.score
group by s1.sid,s1.cid,s1.score
having rank <=2
order by s1.cid,rank;
mysql> select
-> s1.*,
-> count(distinct(s2.score)) rank
-> from sc s1
-> join sc s2 on s1.cid = s2.cid and s1.score <= s2.score
-> group by s1.sid,s1.cid,s1.score
-> having rank <=2
-> order by s1.cid,rank;
+-----+-----+-------+------+
| sid | cid | score | rank |
+-----+-----+-------+------+
| 01 | 01 | 80.0 | 1 |
| 03 | 01 | 80.0 | 1 |
| 05 | 01 | 76.0 | 2 |
| 01 | 02 | 90.0 | 1 |
| 07 | 02 | 89.0 | 2 |
| 01 | 03 | 99.0 | 1 |
| 07 | 03 | 98.0 | 2 |
+-----+-----+-------+------+
7 rows in set (0.00 sec)
select
stu.sname,
c.cname,
t.tname,
s1.score,
count(distinct(s2.score)) rank
from sc s1
join sc s2 on s1.cid = s2.cid and s1.score <= s2.score
join student stu on s1.sid = stu.sid
join course c on s1.cid = c.cid
join teacher t on c.tid = t.tid
group by s1.sid,s1.cid,s1.score
having rank <=2
order by s1.cid,rank;
mysql> select
-> stu.sname,
-> c.cname,
-> t.tname,
-> s1.score,
-> count(distinct(s2.score)) rank
-> from sc s1
-> join sc s2 on s1.cid = s2.cid and s1.score <= s2.score
-> join student stu on s1.sid = stu.sid
-> join course c on s1.cid = c.cid
-> join teacher t on c.tid = t.tid
-> group by s1.sid,s1.cid,s1.score
-> having rank <=2
-> order by s1.cid,rank;
+--------+--------+--------+-------+------+
| sname | cname | tname | score | rank |
+--------+--------+--------+-------+------+
| 孙风 | 语文 | 李四 | 80.0 | 1 |
| 赵雷 | 语文 | 李四 | 80.0 | 1 |
| 周梅 | 语文 | 李四 | 76.0 | 2 |
| 赵雷 | 数学 | 张三 | 90.0 | 1 |
| 郑竹 | 数学 | 张三 | 89.0 | 2 |
| 赵雷 | 英语 | 王五 | 99.0 | 1 |
| 郑竹 | 英语 | 王五 | 98.0 | 2 |
+--------+--------+--------+-------+------+
7 rows in set (0.00 sec)
select
s1.*
from sc s1
where (select count(1) -- count(1)类似count(*):统计表s2中分数大的数量
from sc s2
where s2.cid=s1.cid -- 课程相同
and s2.score >= s1.score) <= 2 -- 前2名
order by s1.cid;
此方法有缺陷，重复分数未统计
mysql> select
-> s1.*
-> from sc s1
-> where (select count(1) -- count(1)类似count(*):统计表s2中分数大的数量
-> from sc s2
-> where s2.cid=s1.cid -- 课程相同
-> and s2.score >= s1.score) <= 2 -- 前2名
-> order by s1.cid;
+-----+-----+-------+
| sid | cid | score |
+-----+-----+-------+
| 01 | 01 | 80.0 |
| 03 | 01 | 80.0 |
| 01 | 02 | 90.0 |
| 07 | 02 | 89.0 |
| 01 | 03 | 99.0 |
| 07 | 03 | 98.0 |
+-----+-----+-------+
6 rows in set (0.00 sec)
select
s1.*
from sc s1
where (select count(distinct(s2.score)) -- 根据分数去重并统计表s2中分数大的数量
from sc s2
where s2.cid=s1.cid -- 课程相同
and s2.score >= s1.score) <= 2 -- 前2名
order by s1.cid;
mysql> select
-> s1.*
-> from sc s1
-> where (select count(distinct(s2.score)) -- 根据分数去重并统计表s2中分数大的数量
-> from sc s2
-> where s2.cid=s1.cid -- 课程相同
-> and s2.score >= s1.score) <= 2 -- 前2名
-> order by s1.cid;
+-----+-----+-------+
| sid | cid | score |
+-----+-----+-------+
| 01 | 01 | 80.0 |
| 03 | 01 | 80.0 |
| 05 | 01 | 76.0 |
| 01 | 02 | 90.0 |
| 07 | 02 | 89.0 |
| 01 | 03 | 99.0 |
| 07 | 03 | 98.0 |
+-----+-----+-------+
7 rows in set (0.00 sec)
4.43、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。
select
sc.cid '课程号',
c.cname '课程名',
count(*) '选修人数'
from sc
join course c on sc.cid = c.cid
group by sc.cid
having(count(*)) > 5;
mysql> select
-> sc.cid '课程号',
-> c.cname '课程名',
-> count(*) '选修人数'
-> from sc
-> join course c on sc.cid = c.cid
-> group by sc.cid
-> having(count(*)) > 5;
+-----------+-----------+--------------+
| 课程号 | 课程名 | 选修人数 |
+-----------+-----------+--------------+
| 01 | 语文 | 6 |
| 02 | 数学 | 6 |
| 03 | 英语 | 6 |
+-----------+-----------+--------------+
3 rows in set (0.00 sec)
4.44、检索至少选修两门课程的学生学号
select
sc.sid,
stu.sname,
count(*)
from sc
join student stu on sc.sid = stu.sid
group by sc.sid
having count(*) >= 2;
mysql> select
-> sc.sid,
-> stu.sname,
-> count(*)
-> from sc
-> join student stu on sc.sid = stu.sid
-> group by sc.sid
-> having count(*) >= 2;
+-----+--------+----------+
| sid | sname | count(*) |
+-----+--------+----------+
| 01 | 赵雷 | 3 |
| 02 | 钱电 | 3 |
| 03 | 孙风 | 3 |
| 04 | 李云 | 3 |
| 05 | 周梅 | 2 |
| 06 | 吴兰 | 2 |
| 07 | 郑竹 | 2 |
+-----+--------+----------+
7 rows in set (0.00 sec)
4.45、查询选修了全部课程的学生信息
select
sc.sid,
stu.sname,
count(*)
from sc
join student stu on sc.sid = stu.sid
group by sc.sid
having count(*) = (select count(*) from course);
mysql> select
-> sc.sid,
-> stu.sname,
-> count(*)
-> from sc
-> join student stu on sc.sid = stu.sid
-> group by sc.sid
-> having count(*) = (select count(*) from course);
+-----+--------+----------+
| sid | sname | count(*) |
+-----+--------+----------+
| 01 | 赵雷 | 3 |
| 02 | 钱电 | 3 |
| 03 | 孙风 | 3 |
| 04 | 李云 | 3 |
+-----+--------+----------+
4 rows in set (0.00 sec)
4.46、查询各学生的年龄
-- 通过date_format函数能够指定返回的数据
select year(now());
select date_format(now(), '%Y');
select date_format(now(), '%Y-%m-%d');
mysql> select year(now());
+-------------+
| year(now()) |
+-------------+
| 2024 |
+-------------+
1 row in set (0.00 sec)
mysql> select date_format(now(), '%Y');
+--------------------------+
| date_format(now(), '%Y') |
+--------------------------+
| 2024 |
+--------------------------+
1 row in set (0.00 sec)
mysql> select date_format(now(), '%Y-%m-%d');
+--------------------------------+
| date_format(now(), '%Y-%m-%d') |
+--------------------------------+
| 2024-02-08 |
+--------------------------------+
1 row in set (0.00 sec)
select
stu.sname '姓名',
TIMESTAMPDIFF(year,stu.sage,now()) '年龄' -- TIMESTAMPDIFF函数返回年差
from student stu;
mysql> select
-> stu.sname '姓名',
-> TIMESTAMPDIFF(year,stu.sage,now()) '年龄'
-> from student stu;
+--------+--------+
| 姓名 | 年龄 |
+--------+--------+
| 赵雷 | 34 |
| 钱电 | 33 |
| 孙风 | 33 |
| 李云 | 33 |
| 周梅 | 32 |
| 吴兰 | 31 |
| 郑竹 | 34 |
| 王菊 | 34 |
+--------+--------+
8 rows in set (0.00 sec)
select
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 age -- 当前日期大，说明已经过生了，年龄正常；反之说明今年还没有到年龄-1
from student;
mysql> select
-> 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 age -- 当前日 期大，说明已经过生了，年龄正常；反之说明今年还没有到年龄-1
-> from student;
+--------+---------------------+------+
| sname | sage | age |
+--------+---------------------+------+
| 赵雷 | 1990-01-01 00:00:00 | 34 |
| 钱电 | 1990-12-21 00:00:00 | 33 |
| 孙风 | 1990-05-20 00:00:00 | 33 |
| 李云 | 1990-08-06 00:00:00 | 33 |
| 周梅 | 1991-12-01 00:00:00 | 32 |
| 吴兰 | 1992-03-01 00:00:00 | 31 |
| 郑竹 | 1989-07-01 00:00:00 | 34 |
| 王菊 | 1990-01-20 00:00:00 | 34 |
+--------+---------------------+------+
8 rows in set (0.00 sec)
4.47、查询本周过生日的学生
INSERT INTO student VALUES('09' , '李白' , date_format(now(),'%Y-%m-%d'), '男'),
('10' , '玛利亚' , date_format(now(),'%Y-%m-%d'), '女');
select * from student;
mysql> INSERT INTO student VALUES('09' , '李白' , date_format(now(),'%Y-%m-%d'), '男'),
-> ('10' , '玛利亚' , date_format(now(),'%Y-%m-%d'), '女');
Query OK, 2 rows affected (0.00 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql>
mysql> select * from student;
+-----+-----------+---------------------+------+
| sid | sname | sage | ssex |
+-----+-----------+---------------------+------+
| 01 | 赵雷 | 1990-01-01 00:00:00 | 男 |
| 02 | 钱电 | 1990-12-21 00:00:00 | 男 |
| 03 | 孙风 | 1990-05-20 00:00:00 | 男 |
| 04 | 李云 | 1990-08-06 00:00:00 | 男 |
| 05 | 周梅 | 1991-12-01 00:00:00 | 女 |
| 06 | 吴兰 | 1992-03-01 00:00:00 | 女 |
| 07 | 郑竹 | 1989-07-01 00:00:00 | 女 |
| 08 | 王菊 | 1990-01-20 00:00:00 | 女 |
| 09 | 李白 | 2024-02-08 00:00:00 | 男 |
| 10 | 玛利亚 | 2024-02-08 00:00:00 | 女 |
+-----+-----------+---------------------+------+
10 rows in set (0.01 sec)
select
stu.*
from student stu
where week(date_format(now(),'%Y%m%d')) = week(sage);
mysql> select
-> stu.*
-> from student stu
-> where week(date_format(now(),'%Y%m%d')) = week(sage);
+-----+-----------+---------------------+------+
| sid | sname | sage | ssex |
+-----+-----------+---------------------+------+
| 09 | 李白 | 2024-02-08 00:00:00 | 男 |
| 10 | 玛利亚 | 2024-02-08 00:00:00 | 女 |
+-----+-----------+---------------------+------+
2 rows in set (0.00 sec)
select * from student where WEEKOFYEAR(NOW())-WEEKOFYEAR(sage)=0;
mysql> select * from student where WEEKOFYEAR(NOW())-WEEKOFYEAR(sage)=0;
+-----+-----------+---------------------+------+
| sid | sname | sage | ssex |
+-----+-----------+---------------------+------+
| 09 | 李白 | 2024-02-08 00:00:00 | 男 |
| 10 | 玛利亚 | 2024-02-08 00:00:00 | 女 |
+-----+-----------+---------------------+------+
2 rows in set (0.00 sec)
4.48、查询下周过生日的学生
select
stu.*
from student stu
where week(date_format(now(),'%Y%m%d'))+1 = week(sage);
select * from student where WEEKOFYEAR(NOW())-WEEKOFYEAR(sage)=-1;
4.49、查询本月过生日的学生
select
stu.*
from student stu
where month(date_format(now(),'%Y%m%d')) = month(sage);
mysql> select
-> stu.*
-> from student stu
-> where month(date_format(now(),'%Y%m%d')) = month(sage);
+-----+-----------+---------------------+------+
| sid | sname | sage | ssex |
+-----+-----------+---------------------+------+
| 09 | 李白 | 2024-02-08 00:00:00 | 男 |
| 10 | 玛利亚 | 2024-02-08 00:00:00 | 女 |
+-----+-----------+---------------------+------+
2 rows in set (0.00 sec)
4.50、查询下月过生日的学生
select
stu.*
from student stu
where month(date_format(now(),'%Y%m%d'))+1 = month(sage);
mysql> select
-> stu.*
-> from student stu
-> where month(date_format(now(),'%Y%m%d'))+1 = month(sage);
+-----+--------+---------------------+------+
| sid | sname | sage | ssex |
+-----+--------+---------------------+------+
| 06 | 吴兰 | 1992-03-01 00:00:00 | 女 |
+-----+--------+---------------------+------+
1 row in set (0.00 sec)
-- 假设现在是12月份，那么下个月就是明年的1月份,解决：当前月份与12的余数
select
stu.*
from student stu
where mod(month(now()),12)+1 = month(sage);
mysql> select
-> stu.*
-> from student stu
-> where mod(month(now()),12)+1 = month(sage);
+-----+--------+---------------------+------+
| sid | sname | sage | ssex |
+-----+--------+---------------------+------+
| 06 | 吴兰 | 1992-03-01 00:00:00 | 女 |
+-----+--------+---------------------+------+
1 row in set (0.00 sec)