sql语句课程练习（2）

心已赠人 2023-10-06 17:50 41阅读 0赞

#### sql语句课程练习（2） ####

*  表结构
 *   *  1、查询"01"课程比"02"课程成绩高的学生的信息及课程分数
     *  2、查询平均成绩大于等于60分的同学的学生编号和学生姓名和平均成绩
     *  3、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-- (包括有成绩的和无成绩的)
     *  4、查询所有同学的学生编号、学生姓名、选课总数、所有课程的总成绩
     *  5、查询学过"张三"老师授课的同学的信息
     *  6、查询没学过"张三"老师授课的同学的信息
     *  7、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
     *  8、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
     *  9、查询没有学全所有课程的同学的信息
     *  10、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
     *  11、查询没学过"张三"老师讲授的任一门课程的学生姓名
     *  12、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
     *  13、检索"01"课程分数小于60，按分数降序排列的学生信息
     *  14、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
     *  15、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
     *   *  case具有两种格式
         *   *  1、简单函数的运用
             *  2、Case搜索函数写法(注意sex的位置【推荐】)
     *  16、查询各科成绩最高分、最低分和平均分：以如下形式显示：课程ID，课程name，最高分，最低分，平均分，及格率，中等率，优良率，优秀率--及格为>=60，中等为：70-80，优良为：80-90，优秀为：>=90
     *  17、按各科成绩进行排序，并显示排名
     *   *  Mysql中（@i:=@i+1）的作用
     *  18、查询学生的总成绩并进行排名
     *  19、查询不同老师所教不同课程平均分从高到低显示
     *  20、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
     *  21、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
     *  22、查询学生平均成绩及其名次
     *  23、查询各科成绩前三名的记录
     *  24、查询每门课程被选修的学生数
     *  25、查询出只有两门课程的全部学生的学号和姓名
     *  26、查询男生、女生人数
     *  27、查询同名同性学生名单，并统计同名人数
     *  28、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
     *  29、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
     *  30、查询课程名称为"数学"，且分数低于60的学生姓名和分数
     *  31、查询所有学生的课程及分数情况；
     *  32、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
     *  33、查询不及格的课程
     *  34、查询课程编号为01且课程成绩在80分以上的学生的学号和姓名
     *  35、求每门课程的学生人数
     *  36、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
     *  37、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
     *  38、查询每门功课成绩最好的前两名
     *  39、统计每门课程的学生选修人数（超过5人的课程才统计）。要求输出课程号和选修人数，查询结果按人数降序排列，若人数相同，按课程号升序排列
     *  40、检索至少选修两门课程的学生学号
     *  41、查询各学生的年龄
     *  42、查询下周过生日的学生
     *  43、查询本月过生日的学生
     *  44、查询下月过生日的学生

## 表结构 ##

表名和字段

–1.学生表  
Student(s\_id,s\_name,s\_birth,s\_sex) --学生编号,学生姓名, 出生年月,学生性别

–2.课程表  
Course(c\_id,c\_name,t\_id) – --课程编号, 课程名称, 教师编号

–3.教师表  
Teacher(t\_id,t\_name) --教师编号,教师姓名

–4.成绩表  
Score(s\_id,c\_id,s\_score) --学生编号,课程编号,分数

CREATE TABLE `Course` (
      `c_id` varchar(20) NOT NULL COMMENT '课程编号',
      `c_name` varchar(20) NOT NULL DEFAULT '' COMMENT '课程名称',
      `t_id` varchar(20) NOT NULL COMMENT '教师编号',
      PRIMARY KEY (`c_id`)
    ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='课程表';
    
    INSERT INTO `mysqldemo`.`Course` (`c_id`, `c_name`, `t_id`) VALUES ('01', '语文', '02');
    INSERT INTO `mysqldemo`.`Course` (`c_id`, `c_name`, `t_id`) VALUES ('02', '数学', '01');
    INSERT INTO `mysqldemo`.`Course` (`c_id`, `c_name`, `t_id`) VALUES ('03', '英语', '03');
    
    CREATE TABLE `Student` (
      `s_id` varchar(20) NOT NULL COMMENT '学生编号',
      `s_name` varchar(20) NOT NULL DEFAULT '' COMMENT '学生姓名',
      `s_birth` varchar(20) NOT NULL DEFAULT '' COMMENT '出生年月',
      `s_sex` varchar(10) NOT NULL DEFAULT '' COMMENT '学生性别',
      PRIMARY KEY (`s_id`)
    ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='学生表';
    
    INSERT INTO `mysqldemo`.`Student` (`s_id`, `s_name`, `s_birth`, `s_sex`) VALUES ('01', '赵雷', '1990-01-01', '男');
    INSERT INTO `mysqldemo`.`Student` (`s_id`, `s_name`, `s_birth`, `s_sex`) VALUES ('02', '钱电', '1990-12-21', '男');
    INSERT INTO `mysqldemo`.`Student` (`s_id`, `s_name`, `s_birth`, `s_sex`) VALUES ('03', '孙风', '1990-05-20', '男');
    INSERT INTO `mysqldemo`.`Student` (`s_id`, `s_name`, `s_birth`, `s_sex`) VALUES ('04', '李云', '1990-08-06', '男');
    INSERT INTO `mysqldemo`.`Student` (`s_id`, `s_name`, `s_birth`, `s_sex`) VALUES ('05', '周梅', '1991-12-01', '女');
    INSERT INTO `mysqldemo`.`Student` (`s_id`, `s_name`, `s_birth`, `s_sex`) VALUES ('06', '吴兰', '1992-03-01', '女');
    INSERT INTO `mysqldemo`.`Student` (`s_id`, `s_name`, `s_birth`, `s_sex`) VALUES ('07', '郑竹', '1989-07-01', '女');
    INSERT INTO `mysqldemo`.`Student` (`s_id`, `s_name`, `s_birth`, `s_sex`) VALUES ('08', '王菊', '1990-01-20', '女');
    
    CREATE TABLE `Teacher` (
      `t_id` varchar(20) NOT NULL COMMENT '教师编号',
      `t_name` varchar(20) NOT NULL DEFAULT '' COMMENT '教师姓名',
      PRIMARY KEY (`t_id`)
    ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='教师表';
    
    INSERT INTO `mysqldemo`.`Teacher` (`t_id`, `t_name`) VALUES ('01', '张三');
    INSERT INTO `mysqldemo`.`Teacher` (`t_id`, `t_name`) VALUES ('02', '李四');
    INSERT INTO `mysqldemo`.`Teacher` (`t_id`, `t_name`) VALUES ('03', '王五');
    
    CREATE TABLE `Score` (
      `s_id` varchar(20) NOT NULL COMMENT '学生编号',
      `c_id` varchar(20) NOT NULL COMMENT '课程编号',
      `s_score` int(3) DEFAULT NULL COMMENT '分数',
      PRIMARY KEY (`s_id`,`c_id`)
    ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='成绩表';
    
    INSERT INTO `mysqldemo`.`Score` (`s_id`, `c_id`, `s_score`) VALUES ('01', '01', '80');
    INSERT INTO `mysqldemo`.`Score` (`s_id`, `c_id`, `s_score`) VALUES ('01', '02', '90');
    INSERT INTO `mysqldemo`.`Score` (`s_id`, `c_id`, `s_score`) VALUES ('01', '03', '99');
    INSERT INTO `mysqldemo`.`Score` (`s_id`, `c_id`, `s_score`) VALUES ('02', '01', '70');
    INSERT INTO `mysqldemo`.`Score` (`s_id`, `c_id`, `s_score`) VALUES ('02', '02', '60');
    INSERT INTO `mysqldemo`.`Score` (`s_id`, `c_id`, `s_score`) VALUES ('02', '03', '80');
    INSERT INTO `mysqldemo`.`Score` (`s_id`, `c_id`, `s_score`) VALUES ('03', '01', '80');
    INSERT INTO `mysqldemo`.`Score` (`s_id`, `c_id`, `s_score`) VALUES ('03', '02', '80');
    INSERT INTO `mysqldemo`.`Score` (`s_id`, `c_id`, `s_score`) VALUES ('03', '03', '80');
    INSERT INTO `mysqldemo`.`Score` (`s_id`, `c_id`, `s_score`) VALUES ('04', '01', '50');
    INSERT INTO `mysqldemo`.`Score` (`s_id`, `c_id`, `s_score`) VALUES ('04', '02', '30');
    INSERT INTO `mysqldemo`.`Score` (`s_id`, `c_id`, `s_score`) VALUES ('04', '03', '20');
    INSERT INTO `mysqldemo`.`Score` (`s_id`, `c_id`, `s_score`) VALUES ('05', '01', '76');
    INSERT INTO `mysqldemo`.`Score` (`s_id`, `c_id`, `s_score`) VALUES ('05', '02', '87');
    INSERT INTO `mysqldemo`.`Score` (`s_id`, `c_id`, `s_score`) VALUES ('06', '01', '31');
    INSERT INTO `mysqldemo`.`Score` (`s_id`, `c_id`, `s_score`) VALUES ('06', '03', '34');
    INSERT INTO `mysqldemo`.`Score` (`s_id`, `c_id`, `s_score`) VALUES ('07', '02', '89');
    INSERT INTO `mysqldemo`.`Score` (`s_id`, `c_id`, `s_score`) VALUES ('07', '03', '98');

### 1、查询"01"课程比"02"课程成绩高的学生的信息及课程分数 ###

第一种方式

select a.* ,b.s_score as 01_score,c.s_score as 02_score from 
    Student a 
    	join Score b on a.s_id=b.s_id and b.c_id='01'
    	left join Score c on a.s_id=c.s_id and c.c_id='02' or c.c_id = NULL where b.s_score>c.s_score

![在这里插入图片描述][202105281033451.png]  
第二种方式

select a.*,b.s_score as 01_score,c.s_score as 02_score from Student a,Score b,Score c 
    		where a.s_id=b.s_id 
    		and a.s_id=c.s_id 
    		and b.c_id='01' 
    		and c.c_id='02' 
    		and b.s_score>c.s_score

![在这里插入图片描述][20210528103512768.png]

### 2、查询平均成绩大于等于60分的同学的学生编号和学生姓名和平均成绩 ###

select b.s_id,b.s_name,ROUND(AVG(a.s_score),2) as avg_score from 
    	Student b 
    	join Score a on b.s_id = a.s_id
    	GROUP BY b.s_id,b.s_name HAVING avg_score >=60;

![在这里插入图片描述][20210528103831722.png]

### 3、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-- (包括有成绩的和无成绩的) ###

select b.s_id,b.s_name,ROUND(AVG(a.s_score),2) as avg_score from 
    	Student b 
    	left join Score a on b.s_id = a.s_id
    	GROUP BY b.s_id,b.s_name HAVING avg_score <60
    	union
    select a.s_id,a.s_name,0 as avg_score from 
    	Student a 
    	where a.s_id not in (
    				select distinct s_id from Score);

![在这里插入图片描述][20210528104138971.png]

### 4、查询所有同学的学生编号、学生姓名、选课总数、所有课程的总成绩 ###

select a.s_id,a.s_name,count(b.c_id) as sum_course,sum(b.s_score) as sum_score from 
    	Student a 
    	left join Score b on a.s_id=b.s_id
    	GROUP BY a.s_id,a.s_name;

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaWd1YW5nMTAy_size_16_color_FFFFFF_t_70]

### 5、查询学过"张三"老师授课的同学的信息 ###

select a.* from 
    	Student a 
    	join Score b on a.s_id=b.s_id where b.c_id in(
    		select c_id from Course where t_id =(
    			select t_id from Teacher where t_name = '张三'));

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaWd1YW5nMTAy_size_16_color_FFFFFF_t_70 1]

### 6、查询没学过"张三"老师授课的同学的信息 ###

select * from 
        Student c 
        where c.s_id not in(
            select a.s_id from Student a join Score b on a.s_id=b.s_id where b.c_id in(
            select a.c_id from Course a join Teacher b on a.t_id = b.t_id where t_name ='张三'));

![在这里插入图片描述][20210528104932802.png]

### 7、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 a.* from 
    	Student a,Score b,Score c 
    	where a.s_id = b.s_id  and a.s_id = c.s_id and b.c_id='01' and c.c_id='02';

![在这里插入图片描述][20210528105108317.png]

### 8、查询学过编号为"01"但是没有学过编号为"02"的课程的同学的信息 ###

select a.* from 
    	Student a 
    	where a.s_id in (select s_id from Score where c_id='01' ) and a.s_id not in(select s_id from Score where c_id='02')

![在这里插入图片描述][20210528105306817.png]

### 9、查询没有学全所有课程的同学的信息 ###

select s.* from Student s 
    left join Score s1 on s1.s_id=s.s_id
    group by s.s_id having count(s1.c_id)<(select count(*) from Course)

![在这里插入图片描述][20210528105722273.png]

select * from Student
    where s_id not in(
    select s_id from Score t1  
    group by s_id having count(*) =(select count(distinct c_id)  from Course))

![在这里插入图片描述][20210528105740456.png]

### 10、查询至少有一门课与学号为"01"的同学所学相同的同学的信息 ###

select * from Student where s_id in(
    	select distinct a.s_id from Score a where a.c_id in(select a.c_id from Score a where a.s_id='01')
    );

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaWd1YW5nMTAy_size_16_color_FFFFFF_t_70 2]

### 11、查询没学过"张三"老师讲授的任一门课程的学生姓名 ###

select a.s_name from Student a where a.s_id not in (
    	select s_id from Score where c_id = 
    				(select c_id from Course where t_id =(
    					select t_id from Teacher where t_name = '张三')));

![在这里插入图片描述][20210528110748637.png]

### 12、查询两门及其以上不及格课程的同学的学号，姓名及其平均成绩 ###

select a.s_id,a.s_name,ROUND(AVG(b.s_score)) from 
    	Student a 
    	left join Score b on a.s_id = b.s_id
    	where a.s_id in(
    			select s_id from Score where s_score<60 GROUP BY  s_id having count(1)>=2)
    	GROUP BY a.s_id,a.s_name

![在这里插入图片描述][20210528110858312.png]

### 13、检索"01"课程分数小于60，按分数降序排列的学生信息 ###

select a.*,b.c_id,b.s_score from 
    	Student a,Score b 
    	where a.s_id = b.s_id and b.c_id='01' and b.s_score<60 ORDER BY b.s_score DESC;

![在这里插入图片描述][20210528111022329.png]

### 14、按平均成绩从高到低显示所有学生的所有课程的成绩以及平均成绩 ###

select a.s_id,(select s_score from Score where s_id=a.s_id and c_id='01') as 语文,
    				(select s_score from Score where s_id=a.s_id and c_id='02') as 数学,
    				(select s_score from Score where s_id=a.s_id and c_id='03') as 英语,
    			round(avg(s_score),2) as 平均分 from Score a  GROUP BY a.s_id ORDER BY 平均分 DESC;

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaWd1YW5nMTAy_size_16_color_FFFFFF_t_70 3]

### 15、按平均成绩从高到低显示所有学生的所有课程的成绩以及平均成绩 ###

SELECT a.s_id,MAX(CASE a.c_id WHEN '01' THEN a.s_score END ) 语文, 
    MAX(CASE a.c_id WHEN '02' THEN a.s_score END ) 数学, 
    MAX(CASE a.c_id WHEN '03' THEN a.s_score END ) 英语, 
    avg(a.s_score),b.s_name FROM Score a JOIN Student b ON a.s_id=b.s_id GROUP BY a.s_id ORDER BY 5 DESC

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaWd1YW5nMTAy_size_16_color_FFFFFF_t_70 4]

#### case具有两种格式 ####

简单函数

CASE \[col\_name\] WHEN \[value1\] THEN \[result1\]…ELSE \[default\] END

搜索函数

CASE WHEN \[expr\] THEN \[result1\]…ELSE \[default\] END

CREATE TABLE `user` (
      `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
      `sex` tinyint(1) DEFAULT '1' COMMENT '性别：0女；1男；2保密',
      `age` int(3) DEFAULT '1' COMMENT '年龄',
      `province` char(254) DEFAULT NULL COMMENT '所在省份',
      PRIMARY KEY (`id`)
    ) ENGINE=MyISAM AUTO_INCREMENT=14 DEFAULT CHARSET=utf8;
    
    INSERT INTO `mysqldemo`.`user` (`id`, `sex`, `age`, `province`) VALUES ('1', '1', '22', '北京');
    INSERT INTO `mysqldemo`.`user` (`id`, `sex`, `age`, `province`) VALUES ('2', '0', '25', '广东');
    INSERT INTO `mysqldemo`.`user` (`id`, `sex`, `age`, `province`) VALUES ('3', '0', '56', '天津');
    INSERT INTO `mysqldemo`.`user` (`id`, `sex`, `age`, `province`) VALUES ('4', '1', '14', '北京');
    INSERT INTO `mysqldemo`.`user` (`id`, `sex`, `age`, `province`) VALUES ('5', '0', '36', '广东');
    INSERT INTO `mysqldemo`.`user` (`id`, `sex`, `age`, `province`) VALUES ('6', '1', '68', '湖南');
    INSERT INTO `mysqldemo`.`user` (`id`, `sex`, `age`, `province`) VALUES ('7', '1', '45', '北京');
    INSERT INTO `mysqldemo`.`user` (`id`, `sex`, `age`, `province`) VALUES ('8', '1', '17', '河北');
    INSERT INTO `mysqldemo`.`user` (`id`, `sex`, `age`, `province`) VALUES ('9', '2', '33', '天津');
    INSERT INTO `mysqldemo`.`user` (`id`, `sex`, `age`, `province`) VALUES ('10', '1', '27', '湖南');
    INSERT INTO `mysqldemo`.`user` (`id`, `sex`, `age`, `province`) VALUES ('11', '1', '29', '北京');
    INSERT INTO `mysqldemo`.`user` (`id`, `sex`, `age`, `province`) VALUES ('12', '2', '70', '广东');
    INSERT INTO `mysqldemo`.`user` (`id`, `sex`, `age`, `province`) VALUES ('13', '0', '24', '北京');

##### 1、简单函数的运用 #####

SELECT
    	 case `username`
    	 when 'admin' then '超级管理员'
    	 when 'admin2' then '2管理'
    	 when 'admin3' then '3管理'
    	 else '其他普通用户' end
    FROM admin_users;

![在这里插入图片描述][20210528113335709.png]

select *,
    (
    	CASE sex WHEN '1' THEN '男' 
    					 WHEN '0' THEN '女' 
    					 ELSE '保密' END) as sex_text from user

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaWd1YW5nMTAy_size_16_color_FFFFFF_t_70 5]

##### 2、Case搜索函数写法(注意sex的位置【推荐】) #####

select *,(
    	CASE WHEN sex='1' THEN '男' 
    			 WHEN sex='0' THEN '女' 
    			 ELSE '保密' END) as sex_text
    from user

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaWd1YW5nMTAy_size_16_color_FFFFFF_t_70 6]  
总结：

简单Case函数写法只适合相等条件判断，不能用于大于、小于及不等于的判断，

Case搜索函数写法适合复杂条件判断：可用于大于、小于及不等于的判断。

### 16、查询各科成绩最高分、最低分和平均分：以如下形式显示：课程ID，课程name，最高分，最低分，平均分，及格率，中等率，优良率，优秀率–及格为>=60，中等为：70-80，优良为：80-90，优秀为：>=90 ###

select a.c_id,b.c_name,MAX(s_score),MIN(s_score),ROUND(AVG(s_score),2),
    	ROUND(100*(SUM(case when a.s_score>=60 then 1 else 0 end)/SUM(case when a.s_score then 1 else 0 end)),2) as 及格率,
    	ROUND(100*(SUM(case when a.s_score>=70 and a.s_score<=80 then 1 else 0 end)/SUM(case when a.s_score then 1 else 0 end)),2) as 中等率,
    	ROUND(100*(SUM(case when a.s_score>=80 and a.s_score<=90 then 1 else 0 end)/SUM(case when a.s_score then 1 else 0 end)),2) as 优良率,
    	ROUND(100*(SUM(case when a.s_score>=90 then 1 else 0 end)/SUM(case when a.s_score then 1 else 0 end)),2) as 优秀率
    	from Score a left join Course b on a.c_id = b.c_id GROUP BY a.c_id,b.c_name

![在这里插入图片描述][20210528115411486.png]

### 17、按各科成绩进行排序，并显示排名 ###

select a.s_id,a.c_id,
            @i:=@i +1 as i保留排名,
            @k:=(case when @score=a.s_score then @k else @i end) as rank不保留排名,
            @score:=a.s_score as score
        from (
            select s_id,c_id,s_score from Score GROUP BY s_id,c_id,s_score ORDER BY s_score DESC
    )a,(select @k:=0,@i:=0,@score:=0)s

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaWd1YW5nMTAy_size_16_color_FFFFFF_t_70 7]

#### Mysql中（@i:=@i+1）的作用 ####

SELECT
    ( @i := @i + 1 ) rownum,age
    FROM
    user,(SELECT @i :=0 ) AS a
    ORDER BY age + 00 DESC

![在这里插入图片描述][20210528121203602.png]

### 18、查询学生的总成绩并进行排名 ###

select a.s_id,
    	@i:=@i+1 as i,
    	@k:=(case when @score=a.sum_score then @k else @i end) as rank,
    	@score:=a.sum_score as Score
    from (select s_id,SUM(s_score) as sum_score from Score GROUP BY s_id ORDER BY sum_score DESC)a,
    	(select @k:=0,@i:=0,@score:=0)s

![在这里插入图片描述][20210528140932624.png]

### 19、查询不同老师所教不同课程平均分从高到低显示 ###

select a.t_id,c.t_name,a.c_id,ROUND(avg(s_score),2) as avg_score from Course a
    		left join Score b on a.c_id=b.c_id 
    		left join Teacher c on a.t_id=c.t_id
    		GROUP BY a.c_id,a.t_id,c.t_name ORDER BY avg_score DESC;

![在这里插入图片描述][20210528141146759.png]

### 20、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 d.*,c.排名,c.s_score,c.c_id from (
    					select a.s_id,a.s_score,a.c_id,@i:=@i+1 as 排名 from Score a,(select @i:=0)s where a.c_id='01'  
    					ORDER BY a.s_score DESC  
    			)c
    			left join Student d on c.s_id=d.s_id
    			where 排名 BETWEEN 2 AND 3
    			UNION
    			select d.*,c.排名,c.s_score,c.c_id from (
    					select a.s_id,a.s_score,a.c_id,@j:=@j+1 as 排名 from Score a,(select @j:=0)s where a.c_id='02'  
    					ORDER BY a.s_score DESC
    			)c
    			left join Student d on c.s_id=d.s_id
    			where 排名 BETWEEN 2 AND 3
    			UNION
    			select d.*,c.排名,c.s_score,c.c_id from (
    					select a.s_id,a.s_score,a.c_id,@k:=@k+1 as 排名 from Score a,(select @k:=0)s where a.c_id='03' 
    					ORDER BY a.s_score DESC
    			)c
    			left join Student d on c.s_id=d.s_id
    			where 排名 BETWEEN 2 AND 3;

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaWd1YW5nMTAy_size_16_color_FFFFFF_t_70 8]

### 21、统计各科成绩各分数段人数：课程编号,课程名称,\[100-85\],\[85-70\],\[70-60\],\[0-60\]及所占百分比 ###

select distinct f.c_name,a.c_id,b.`85-100`,b.百分比,c.`70-85`,c.百分比,d.`60-70`,d.百分比,e.`0-60`,e.百分比 from Score a
    		left join (select c_id,SUM(case when s_score >85 and s_score <=100 then 1 else 0 end) as `85-100`,
    									ROUND(100*(SUM(case when s_score >85 and s_score <=100 then 1 else 0 end)/count(*)),2) as 百分比
    						from Score GROUP BY c_id)b on a.c_id=b.c_id
    		left join (select c_id,SUM(case when s_score >70 and s_score <=85 then 1 else 0 end) as `70-85`,
    									ROUND(100*(SUM(case when s_score >70 and s_score <=85 then 1 else 0 end)/count(*)),2) as 百分比
    						from Score GROUP BY c_id)c on a.c_id=c.c_id
    		left join (select c_id,SUM(case when s_score >60 and s_score <=70 then 1 else 0 end) as `60-70`,
    									ROUND(100*(SUM(case when s_score >60 and s_score <=70 then 1 else 0 end)/count(*)),2) as 百分比
    						from Score GROUP BY c_id)d on a.c_id=d.c_id
    		left join (select c_id,SUM(case when s_score >=0 and s_score <=60 then 1 else 0 end) as `0-60`,
    									ROUND(100*(SUM(case when s_score >=0 and s_score <=60 then 1 else 0 end)/count(*)),2) as 百分比
    						from Score GROUP BY c_id)e on a.c_id=e.c_id
    		left join Course f on a.c_id = f.c_id

![在这里插入图片描述][20210528142103282.png]

### 22、查询学生平均成绩及其名次 ###

select a.s_id,
    	@i:=@i+1 as '不保留空缺排名',
    	@k:=(case when @avg_score=a.avg_s then @k else @i end) as '保留空缺排名',
    	@avg_score:=avg_s as '平均分'
    from (select s_id,ROUND(AVG(s_score),2) as avg_s from Score GROUP BY s_id ORDER BY avg_s DESC)a,(select @avg_score:=0,@i:=0,@k:=0)b;

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaWd1YW5nMTAy_size_16_color_FFFFFF_t_70 9]

### 23、查询各科成绩前三名的记录 ###

-- 1.选出b表比a表成绩大的所有组
    		-- 2.选出比当前id成绩大的 小于三个的

select a.s_id,a.c_id,a.s_score from Score a 
    			left join Score b on a.c_id = b.c_id and a.s_score<b.s_score
    			group by a.s_id,a.c_id,a.s_score HAVING COUNT(b.s_id)<3
    			ORDER BY a.c_id,a.s_score DESC

![在这里插入图片描述][20210528142453314.png]

### 24、查询每门课程被选修的学生数 ###

select c_id,count(s_id) from Score a GROUP BY c_id

![在这里插入图片描述][20210528142647853.png]

### 25、查询出只有两门课程的全部学生的学号和姓名 ###

select s_id,s_name from Student where s_id in(
      select s_id from Score GROUP BY s_id HAVING COUNT(c_id)=2);

![在这里插入图片描述][20210528142822889.png]

### 26、查询男生、女生人数 ###

select s_sex,COUNT(s_sex) as 人数  from Student GROUP BY s_sex

![在这里插入图片描述][20210528143013823.png]

### 27、查询同名同性学生名单，并统计同名人数 ###

select a.s_name,a.s_sex,count(*) from Student a  JOIN 
    	Student b on a.s_id !=b.s_id and a.s_name = b.s_name and a.s_sex = b.s_sex
    		GROUP BY a.s_name,a.s_sex

![在这里插入图片描述][20210528143440155.png]

### 28、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 c_id,ROUND(AVG(s_score),2) as avg_score from Score 
    GROUP BY c_id ORDER BY avg_score DESC,c_id ASC

![在这里插入图片描述][2021052814363898.png]

### 29、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 a.s_id,b.s_name,ROUND(avg(a.s_score),2) as avg_score from Score a
    		left join Student b on a.s_id=b.s_id GROUP BY s_id HAVING avg_score>=85

![在这里插入图片描述][20210528143822345.png]

### 30、查询课程名称为"数学"，且分数低于60的学生姓名和分数 ###

select a.s_name,b.s_score from Score b join Student a on a.s_id=b.s_id where b.c_id=(
    		select c_id from Course where c_name ='数学') and b.s_score<60

![在这里插入图片描述][20210528144017231.png]

### 31、查询所有学生的课程及分数情况； ###

select a.s_id,a.s_name,
    			SUM(case c.c_name when '语文' then b.s_score else 0 end) as '语文',
    			SUM(case c.c_name when '数学' then b.s_score else 0 end) as '数学',
    			SUM(case c.c_name when '英语' then b.s_score else 0 end) as '英语',
    			SUM(b.s_score) as  '总分'
    from Student a left join Score b on a.s_id = b.s_id 
    left join Course c on b.c_id = c.c_id 
    GROUP BY a.s_id,a.s_name

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaWd1YW5nMTAy_size_16_color_FFFFFF_t_70 10]

### 32、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 a.s_name,b.c_name,c.s_score from Course b left join Score c on b.c_id = c.c_id
    				left join Student a on a.s_id=c.s_id where c.s_score>=70

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaWd1YW5nMTAy_size_16_color_FFFFFF_t_70 11]

### 33、查询不及格的课程 ###

select a.s_id,a.c_id,b.c_name,a.s_score from Score a 
    	left join Course b on a.c_id = b.c_id
    	where a.s_score<60

![在这里插入图片描述][2021052814474826.png]

### 34、查询课程编号为01且课程成绩在80分以上的学生的学号和姓名 ###

select a.s_id,b.s_name from Score a 
    		LEFT JOIN Student b on a.s_id = b.s_id
    		where a.c_id = '01'	and a.s_score>80

![在这里插入图片描述][20210528145119605.png]

### 35、求每门课程的学生人数 ###

select count(*) from Score GROUP BY c_id;

![在这里插入图片描述][20210528145231779.png]

### 36、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 a.*,b.s_score,b.c_id,c.c_name from Student a
    LEFT JOIN Score b on a.s_id = b.s_id
    LEFT JOIN Course c on b.c_id=c.c_id
    where b.c_id =(select c_id from Course c,Teacher d where c.t_id=d.t_id and d.t_name='张三')
    and b.s_score in (select MAX(s_score) from Score where c_id='02')

![在这里插入图片描述][20210528145454227.png]

### 37、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 b.s_id,b.c_id,b.s_score 
    	   from Score a,Score b 
    	   where a.c_id != b.c_id and a.s_score = b.s_score

![在这里插入图片描述][20210528145723623.png]

### 38、查询每门功课成绩最好的前两名 ###

-- 牛逼的写法

select a.s_id,a.c_id,a.s_score from Score a
    		where (select COUNT(1) from Score b where b.c_id=a.c_id and b.s_score>=a.s_score)<=2 ORDER BY a.c_id

![在这里插入图片描述][20210528150215172.png]

### 39、统计每门课程的学生选修人数（超过5人的课程才统计）。要求输出课程号和选修人数，查询结果按人数降序排列，若人数相同，按课程号升序排列 ###

select c_id,count(*) as total from Score GROUP BY c_id HAVING total>5 ORDER BY total,c_id ASC

![在这里插入图片描述][20210528150331733.png]

### 40、检索至少选修两门课程的学生学号 ###

select s_id,count(*) as sel from Score GROUP BY s_id HAVING sel>=2

![在这里插入图片描述][20210528150823359.png]

### 41、查询各学生的年龄 ###

-- 按照出生日期来算，当前月日 < 出生年月的月日则，年龄减一

select s_birth,(DATE_FORMAT(NOW(),'%Y')-DATE_FORMAT(s_birth,'%Y') - 
    	(case when DATE_FORMAT(NOW(),'%m%d')>DATE_FORMAT(s_birth,'%m%d') then 0 else 1 end)) as age
    from Student;

![在这里插入图片描述][20210528151724997.png]

### 42、查询下周过生日的学生 ###

select * from Student where WEEK(DATE_FORMAT(NOW(),'%Y%m%d'))+1 =WEEK(s_birth)

![在这里插入图片描述][20210528152010970.png]

### 43、查询本月过生日的学生 ###

select * from Student where MONTH(DATE_FORMAT(NOW(),'%Y%m%d')) =MONTH(s_birth)

![在这里插入图片描述][2021052815211812.png]

### 44、查询下月过生日的学生 ###

select * from Student where MONTH(DATE_FORMAT(NOW(),'%Y%m%d'))+1 =MONTH(s_birth)

![在这里插入图片描述][20210528152211803.png]

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