90-practice

1. 行转列

+----------+--------+
|rq        |shengfu |
+----------+--------+
|2005-05-09|胜      |
|2005-05-09|胜      |
|2005-05-09|负      |
|2005-05-09|负      |
|2005-05-10|胜      |
|2005-05-10|负      |
|2005-05-10|负      |
+----------+--------+


+----------+--+---+
|rq        |胜|负 |
+----------+--+---+
|2005-05-09|4 |4  |
|2005-05-10|3 |3  |
+----------+--+---+

create table tmp
(
    rq      varchar(10),
    shengfu varbinary(5)
);


insert into tmp values ('2005-05-09', '胜');
insert into tmp values ('2005-05-09', '胜');
insert into tmp values ('2005-05-09', '负');
insert into tmp values ('2005-05-09', '负');
insert into tmp values ('2005-05-10', '胜');
insert into tmp values ('2005-05-10', '负');
insert into tmp values ('2005-05-10', '负');


select rq, if(shengfu, '胜', 1), if(shengfu, '负', 2)
from tmp;

select rq,
       count(if(shengfu, '胜', 1)) 胜,
       count(if(shengfu, '负', 2)) 负
from tmp
group by rq;

+----+-------+-----+
|name|subject|score|
+----+-------+-----+
|张三  |语文  |78   |
|张三  |数学  |88   |
|张三  |英语  |98   |
|李四  |语文  |89   |
|李四  |数学  |76   |
|李四  |英语  |90   |
|王五  |语文  |99   |
|王五  |数学  |66   |
|王五  |英语  |91   |
+----+-------+-----+

+----+----+---+---+
|name|语文|数学|英语|
+----+----+---+---+
|张三 |78  |88 |98 |
|李四 |89  |76 |90 |
|王五 |99  |66 |91 |
+----+----+---+---+

create table student_score
(
    name    varchar(20),
    subject varchar(20),
    score   double(4, 1)
);
insert into student_score (NAME, SUBJECT, SCORE) values ('张三', '语文', 78.0);
insert into student_score (NAME, SUBJECT, SCORE) values ('张三', '数学', 88.0);
insert into student_score (NAME, SUBJECT, SCORE) values ('张三', '英语', 98.0);
insert into student_score (NAME, SUBJECT, SCORE) values ('李四', '语文', 89.0);
insert into student_score (NAME, SUBJECT, SCORE) values ('李四', '数学', 76.0);
insert into student_score (NAME, SUBJECT, SCORE) values ('李四', '英语', 90.0);
insert into student_score (NAME, SUBJECT, SCORE) values ('王五', '语文', 99.0);
insert into student_score (NAME, SUBJECT, SCORE) values ('王五', '数学', 66.0);
insert into student_score (NAME, SUBJECT, SCORE) values ('王五', '英语', 91.0);


# 至少使用4中方式下写出
select ss.name,
       max(if(ss.subject, '语文', ss.score)) 语文,
       max(if(ss.subject, '数学', ss.score)) 数学,
       max(if(ss.subject, '英语', ss.score)) 英语
from student_score ss
group by ss.name;

# case when
select ss.name,
       max(case ss.subject
               when '语文' then
                   ss.score
           end) 语文,
       max(case ss.subject
               when '数学' then
                   ss.score
           end) 数学,
       max(case ss.subject
               when '英语' then
                   ss.score
           end) 英语
from student_score ss
group by ss.name;

# join
select ss.name, ss.score
from student_score ss
where ss.subject = '语文';

select ss.name, ss.score
from student_score ss
where ss.subject = '数学';

select ss.name, ss.score
from student_score ss
where ss.subject = '英语';

select ss1.name, ss1.score 语文, ss2.score 数学, ss3.score 英语
from (select ss.name, ss.score
      from student_score ss
      where ss.subject = '语文') ss1
         join (select ss.name, ss.score
               from student_score ss
               where ss.subject = '数学') ss2
              on ss1.name = ss2.name
         join (select ss.name, ss.score
               from student_score ss
               where ss.subject = '英语') ss3
              on ss1.name = ss3.name;

# union all
select t.name, sum(t.语文), sum(t.数学), sum(t.英语)
from (select ss1.name, ss1.score 语文, 0 数学, 0 英语
      from student_score ss1
      where ss1.subject = '语文'
      union all
      select ss2.name, 0 语文, ss2.score 数学, 0 英语
      from student_score ss2
      where ss2.subject = '数学'
      union all
      select ss3.name, 0 语文, 0 数学, ss3.score 英语
      from student_score ss3
      where ss3.subject = '英语') t
group by t.name;

2. 练习

1. 表结构、数据

-- 学生表
create table student
(
    s_id    varchar(20)            not null comment '学生编号' primary key,
    s_name  varchar(20) default '' not null comment '学生姓名',
    s_birth varchar(20) default '' not null comment '出生年月',
    s_sex   varchar(10) default '' not null comment '学生性别 '
)
    charset = utf8;

-- 课程表
create table course
(
    c_id   varchar(20)            not null comment '课程编号' primary key,
    c_name varchar(20) default '' not null comment '课程名称',
    t_id   varchar(20)            not null comment '教师编号'
)
    charset = utf8;

-- 教师表
create table teacher
(
    t_id   varchar(20)            not null comment '教师编号' primary key,
    t_name varchar(20) default '' not null comment '教师姓名'
)
    charset = utf8;

-- 成绩表
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)      null comment '分数',
    primary key (s_id, c_id)
)
    charset = utf8;

-- 插入学生表测试数据
insert into student values ('01', '赵雷', '1990-01-01', '男');
insert into student values ('02', '钱电', '1990-12-21', '男');
insert into student values ('03', '孙风', '1990-05-20', '男');
insert into student values ('04', '李云', '1990-08-06', '男');
insert into student values ('05', '周梅', '1991-12-01', '女');
insert into student values ('06', '吴兰', '1992-03-01', '女');
insert into student values ('07', '郑竹', '1989-07-01', '女');
insert into student values ('08', '王菊', '1990-01-20', '女');
-- 课程表测试数据
insert into course values ('01', '语文', '02');
insert into course values ('02', '数学', '01');
insert into course values ('03', '英语', '03');
-- 教师表测试数据
insert into teacher values ('01', '张三');
insert into teacher values ('02', '李四');
insert into teacher values ('03', '王五');
-- 成绩表测试数据
insert into score values ('01', '01', 80);
insert into score values ('01', '02', 90);
insert into score values ('01', '03', 99);
insert into score values ('02', '01', 70);
insert into score values ('02', '02', 60);
insert into score values ('02', '03', 80);
insert into score values ('03', '01', 80);
insert into score values ('03', '02', 80);
insert into score values ('03', '03', 80);
insert into score values ('04', '01', 50);
insert into score values ('04', '02', 30);
insert into score values ('04', '03', 20);
insert into score values ('05', '01', 76);
insert into score values ('05', '02', 87);
insert into score values ('06', '01', 31);
insert into score values ('06', '03', 34);
insert into score values ('07', '02', 89);
insert into score values ('07', '03', 98);

2. sql

-- 1. 查询"01"课程比"02"课程成绩高的学生的信息及课程分数
select 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;

+----+------+----------+-----+--------+--------+
|s_id|s_name|s_birth   |s_sex|01_score|02_score|
+----+------+----------+-----+--------+--------+
|02  |钱电   |1990-12-21|男   |70      |60      |
|04  |李云   |1990-08-06|男   |50      |30      |
+----+------+----------+-----+--------+--------+


-- 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 a.*, b.s_score as 01_score, c.s_score as 02_score
from student a
         left join score b on a.s_id = b.s_id and b.c_id = '01' or b.c_id = NULL
         join score c on a.s_id = c.s_id and c.c_id = '02'
where b.s_score < c.s_score;

+----+------+----------+-----+--------+--------+
|s_id|s_name|s_birth   |s_sex|01_score|02_score|
+----+------+----------+-----+--------+--------+
|01  |赵雷   |1990-01-01|男   |80      |90      |
|05  |周梅   |1991-12-01|女   |76      |87      |
+----+------+----------+-----+--------+--------+


-- 3. 查询平均成绩大于等于60分的同学的学生编号和学生姓名和平均成绩
select 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 ROUND(AVG(a.s_score), 2) >= 60;

+----+------+---------+
|s_id|s_name|avg_score|
+----+------+---------+
|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    |
+----+------+---------+


-- 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（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 ROUND(AVG(a.s_score), 2) < 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);

+----+------+---------+
|s_id|s_name|avg_score|
+----+------+---------+
|04  |李云   |33.33    |
|06  |吴兰   |32.50    |
|08  |王菊   |0.00     |
+----+------+---------+


-- 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 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;

+----+------+----------+---------+
|s_id|s_name|sum_course|sum_score|
+----+------+----------+---------+
|01  |赵雷   |3         |269      |
|02  |钱电   |3         |210      |
|03  |孙风   |3         |240      |
|04  |李云   |3         |100      |
|05  |周梅   |2         |163      |
|06  |吴兰   |2         |65       |
|07  |郑竹   |2         |187      |
|08  |王菊   |0         |null     |
+----+------+----------+---------+


-- 6. 查询"李"姓老师的数量
select count(t_id)
from teacher
where t_name like '李%';

+----+------+----------+-----+
|s_id|s_name|s_birth   |s_sex|
+----+------+----------+-----+
|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   |
|07  |郑竹   |1989-07-01|女   |
+----+------+----------+-----+


-- 7. 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'));

+----+------+----------+-----+
|s_id|s_name|s_birth   |s_sex|
+----+------+----------+-----+
|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   |
|07  |郑竹   |1989-07-01|女   |
+----+------+----------+-----+


-- 8. 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 c_id
                                      from course
                                      where t_id = (select t_id
                                                    from teacher
                                                    where t_name = '张三')));

+----+------+----------+-----+
|s_id|s_name|s_birth   |s_sex|
+----+------+----------+-----+
|06  |吴兰   |1992-03-01|女   |
|08  |王菊   |1990-01-20|女   |
+----+------+----------+-----+


-- 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 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';

+----+------+----------+-----+
|s_id|s_name|s_birth   |s_sex|
+----+------+----------+-----+
|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   |
+----+------+----------+-----+


-- 10. 查询学过编号为"01"但是没有学过编号为"02"的课程的同学的信息
select 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');

+----+------+----------+-----+
|s_id|s_name|s_birth   |s_sex|
+----+------+----------+-----+
|06  |吴兰   |1992-03-01|女   |
+----+------+----------+-----+


-- 11. 查询没有学全所有课程的同学的信息
select s.*
from student s
where s.s_id in (select s_id
                 from score
                 where s_id not in (select a.s_id
                                    from score a
                                             join score b on a.s_id = b.s_id and b.c_id = '02'
                                             join score c on a.s_id = c.s_id and c.c_id = '03'
                                    where a.c_id = '01'));

+----+------+----------+-----+
|s_id|s_name|s_birth   |s_sex|
+----+------+----------+-----+
|05  |周梅   |1991-12-01|女   |
|06  |吴兰   |1992-03-01|女   |
|07  |郑竹   |1989-07-01|女   |
+----+------+----------+-----+


-- 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
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'));

+----+------+----------+-----+
|s_id|s_name|s_birth   |s_sex|
+----+------+----------+-----+
|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   |
+----+------+----------+-----+


-- 13. 查询和"01"号的同学学习的课程完全相同的其他同学的信息
select a.*
from student a
where a.s_id in (select distinct s_id
                 from score
                 where s_id != '01'
                   and c_id in (select c_id from score where s_id = '01')
                 group by s_id
                 having count(1) = (select count(1) from score where s_id = '01'));

+----+------+----------+-----+
|s_id|s_name|s_birth   |s_sex|
+----+------+----------+-----+
|02  |钱电   |1990-12-21|男   |
|03  |孙风   |1990-05-20|男   |
|04  |李云   |1990-08-06|男   |
+----+------+----------+-----+


-- 14. 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'))
                     group by s_id);

+------+
|s_name|
+------+
|吴兰   |
|王菊   |
+------+


-- 15. 查询两门及其以上不及格课程的同学的学号，姓名及其平均成绩
select 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;

+----+------+---------------------+
|s_id|s_name|ROUND(AVG(b.s_score))|
+----+------+---------------------+
|04  |李云   |33                   |
|06  |吴兰   |33                   |
+----+------+---------------------+


-- 16. 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;

+----+------+----------+-----+----+-------+
|s_id|s_name|s_birth   |s_sex|c_id|s_score|
+----+------+----------+-----+----+-------+
|04  |李云   |1990-08-06|男   |01  |50     |
|06  |吴兰   |1992-03-01|女   |01  |31     |
+----+------+----------+-----+----+-------+


-- 17. 按平均成绩从高到低显示所有学生的所有课程的成绩以及平均成绩
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;

+----+----+----+----+-----+
|s_id|语文 |数学 |英语|平均分|
+----+----+----+----+-----+
|07  |null|89  |98  |93.50|
|01  |80  |90  |99  |89.67|
|05  |76  |87  |null|81.50|
|03  |80  |80  |80  |80.00|
|02  |70  |60  |80  |70.00|
|04  |50  |30  |20  |33.33|
|06  |31  |null|34  |32.50|
+----+----+----+----+-----+


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

+----+------+------------+------------+----------------------+-----+-----+-----+-----+
|c_id|c_name|MAX(s_score)|MIN(s_score)|ROUND(AVG(s_score), 2)|及格率|中等率|优良率|优秀率|
+----+------+------------+------------+----------------------+-----+-----+-----+-----+
|01  |语文   |80          |31          |64.50                 |66.67|66.67|33.33|0.00 |
|02  |数学   |90          |30          |72.67                 |83.33|16.67|66.67|16.67|
|03  |英语   |99          |20          |68.50                 |66.67|33.33|33.33|33.33|
+----+------+------------+------------+----------------------+-----+-----+-----+-----+


-- 19. 按各科成绩进行排序，并显示排名(实现不完全)。mysql没有rank函数
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 WHERE c_id = '01' GROUP BY s_id, c_id, s_score ORDER BY s_score DESC) a,
     (select @k := 0, @i := 0, @score := 0) s
union
select a.s_id,
       a.c_id,
       @i := @i + 1                                             as i,
       @k := (case when @score = a.s_score then @k else @i end) as 'rank',
       @score := a.s_score                                      as score
from (select s_id, c_id, s_score from score WHERE c_id = '02' GROUP BY s_id, c_id, s_score ORDER BY s_score DESC) a,
     (select @k := 0, @i := 0, @score := 0) s
union
select a.s_id,
       a.c_id,
       @i := @i + 1                                             as i,
       @k := (case when @score = a.s_score then @k else @i end) as 'rank',
       @score := a.s_score                                      as score
from (select s_id, c_id, s_score from score WHERE c_id = '03' GROUP BY s_id, c_id, s_score ORDER BY s_score DESC) a,
     (select @k := 0, @i := 0, @score := 0) s;

+----+----+--------+------------+-----+
|s_id|c_id|i保留排名|rank不保留排名|score|
+----+----+--------+------------+-----+
|01  |01  |1       |1           |80   |
|03  |01  |2       |1           |80   |
|05  |01  |3       |3           |76   |
|02  |01  |4       |4           |70   |
|04  |01  |5       |5           |50   |
|06  |01  |6       |6           |31   |
|01  |02  |7       |7           |90   |
|07  |02  |8       |8           |89   |
|05  |02  |9       |9           |87   |
|03  |02  |10      |10          |80   |
|02  |02  |11      |11          |60   |
|04  |02  |12      |12          |30   |
|01  |03  |13      |13          |99   |
|07  |03  |14      |14          |98   |
|02  |03  |15      |15          |80   |
|03  |03  |16      |15          |80   |
|06  |03  |17      |17          |34   |
|04  |03  |18      |18          |20   |
+----+----+--------+------------+-----+


-- 20. 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;

+----+-+----+-----+
|s_id|i|rank|score|
+----+-+----+-----+
|01  |1|1   |269  |
|03  |2|2   |240  |
|02  |3|3   |210  |
|07  |4|4   |187  |
|05  |5|5   |163  |
|04  |6|6   |100  |
|06  |7|7   |65   |
+----+-+----+-----+


-- 21. 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;

+----+------+----+---------+
|t_id|t_name|c_id|avg_score|
+----+------+----+---------+
|01  |张三   |02  |72.67    |
|03  |王五   |03  |68.50    |
|02  |李四   |01  |64.50    |
+----+------+----+---------+


-- 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 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') 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') 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') c
         left join student d on c.s_id = d.s_id
where 排名 BETWEEN 2 AND 3;

+----+------+----------+-----+--+--------+----+
|s_id|s_name|s_birth   |s_sex|排名|s_score|c_id|
+----+------+----------+-----+--+--------+----+
|02  |钱电   |1990-12-21|男   |2 |70      |01  |
|03  |孙风   |1990-05-20|男   |3 |80      |01  |
|02  |钱电   |1990-12-21|男   |2 |60      |02  |
|03  |孙风   |1990-05-20|男   |3 |80      |02  |
|02  |钱电   |1990-12-21|男   |2 |80      |03  |
|03  |孙风   |1990-05-20|男   |3 |80      |03  |
+----+------+----------+-----+--+--------+----+


-- 23. 统计各科成绩各分数段人数：课程编号,课程名称,[100-85],[85-70],[70-60],[0-60]及所占百分比
select distinct f.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;

+------+----+------+-----+-----+-----+-----+-----+----+-----+
|c_name|c_id|85-100|百分比|70-85|百分比|60-70|百分比|0-60|百分比|
+------+----+------+-----+-----+-----+-----+-----+----+-----+
|语文   |01  |0     |0.00 |3    |50.00|1    |16.67|2   |33.33|
|数学   |02  |3     |50.00|1    |16.67|0    |0.00 |2   |33.33|
|英语   |03  |2     |33.33|2    |33.33|0    |0.00 |2   |33.33|
+------+----+------+-----+-----+-----+-----+-----+----+-----+


-- 24. 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) a,
     (select @avg_score := 0, @i := 0, @k := 0) b;

+----+------------+----------+-----+
|s_id|不保留空缺排名|保留空缺排名|平均分|
+----+------------+----------+-----+
|01  |1           |1         |89.67|
|02  |2           |2         |70.00|
|03  |3           |3         |80.00|
|04  |4           |4         |33.33|
|05  |5           |5         |81.50|
|06  |6           |6         |32.50|
|07  |7           |7         |93.50|
+----+------------+----------+-----+


-- 25. 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;

+----+----+-------+
|s_id|c_id|s_score|
+----+----+-------+
|03  |01  |80     |
|01  |01  |80     |
|05  |01  |76     |
|01  |02  |90     |
|07  |02  |89     |
|05  |02  |87     |
|01  |03  |99     |
|07  |03  |98     |
|03  |03  |80     |
|02  |03  |80     |
+----+----+-------+


-- 26. 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;

+----+-----------+
|c_id|count(s_id)|
+----+-----------+
|01  |6          |
|02  |6          |
|03  |6          |
+----+-----------+


-- 27. 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);

+----+------+
|s_id|s_name|
+----+------+
|05  |周梅   |
|06  |吴兰   |
|07  |郑竹   |
+----+------+


-- 28. 查询男生、女生人数
select s_sex, COUNT(s_sex) as 人数
from student
GROUP BY s_sex;

+-----+---+
|s_sex|人数|
+-----+---+
|女    |4  |
|男    |4  |
+-----+---+


-- 29. 查询名字中含有"风"字的学生信息
select *
from student
where s_name like '%风%';

+----+------+----------+-----+
|s_id|s_name|s_birth   |s_sex|
+----+------+----------+-----+
|03  |孙风   |1990-05-20|男   |
+----+------+----------+-----+


-- 30. 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;

-- 31. 查询1990年出生的学生名单
select s_name
from student
where s_birth like '1990%';

+------+
|s_name|
+------+
|赵雷   |
|钱电   |
|孙风   |
|李云   |
|王菊   |
+------+


-- 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 c_id, ROUND(AVG(s_score), 2) as avg_score
from score
GROUP BY c_id
ORDER BY avg_score DESC, c_id ASC;

+----+---------+
|c_id|avg_score|
+----+---------+
|02  |72.67    |
|03  |68.50    |
|01  |64.50    |
+----+---------+


-- 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 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;

+----+------+---------+
|s_id|s_name|avg_score|
+----+------+---------+
|01  |赵雷   |89.67    |
|07  |郑竹   |93.50    |
+----+------+---------+


-- 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 a.s_name, b.s_score
from score b
         LEFT 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;

+------+-------+
|s_name|s_score|
+------+-------+
|李云   |30     |
+------+-------+


-- 35. 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;

+----+------+---+---+---+-----+
|s_id|s_name|语文|数学|英语|总分 |
+----+------+---+---+---+-----+
|01  |赵雷   |80 |90 |99 |269  |
|02  |钱电   |70 |60 |80 |210  |
|03  |孙风   |80 |80 |80 |240  |
|04  |李云   |50 |30 |20 |100  |
|05  |周梅   |76 |87 |0  |163  |
|06  |吴兰   |31 |0  |34 |65   |
|07  |郑竹   |0  |89 |98 |187  |
|08  |王菊   |0  |0  |0  |nul l|
+----+------+---+---+---+-----+


-- 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 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;

+------+------+-------+
|s_name|c_name|s_score|
+------+------+-------+
|赵雷   |语文  |80     |
|赵雷   |数学  |90     |
|赵雷   |英语  |99     |
|钱电   |语文  |70     |
|钱电   |英语  |80     |
|孙风   |语文  |80     |
|孙风   |数学  |80     |
|孙风   |英语  |80     |
|周梅   |语文  |76     |
|周梅   |数学  |87     |
|郑竹   |数学  |89     |
|郑竹   |英语  |98     |
+------+------+-------+


-- 37. 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;

+----+----+------+-------+
|s_id|c_id|c_name|s_score|
+----+----+------+-------+
|04  |01  |语文   |50     |
|06  |01  |语文   |31     |
|04  |02  |数学   |30     |
|04  |03  |英语   |20     |
|06  |03  |英语   |34     |
+----+----+------+-------+


-- 38. 查询课程编号为01且课程成绩在80分以上的学生的学号和姓名；
select 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;

-- 39. 求每门课程的学生人数
select count(*)
from score
GROUP BY c_id;

+--------+
|count(*)|
+--------+
|6       |
|6       |
|6       |
+--------+


-- 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

-- 查询老师id
select c_id
from course c,
     teacher d
where c.t_id = d.t_id
  and d.t_name = '张三';

-- 查询最高分（可能有相同分数）
select MAX(s_score)
from score
where c_id = '02';

-- 查询信息
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 = (select c_id
                                  from course c,
                                       teacher d
                                  where c.t_id = d.t_id
                                    and d.t_name = '张三'));

+----+------+----------+-----+-------+----+------+
|s_id|s_name|s_birth   |s_sex|s_score|c_id|c_name|
+----+------+----------+-----+-------+----+------+
|01  |赵雷   |1990-01-01|男   |90     |02  |数学   |
+----+------+----------+-----+-------+----+------+


-- 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 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;

+----+----+-------+
|s_id|c_id|s_score|
+----+----+-------+
|01  |01  |80     |
|02  |03  |80     |
|03  |01  |80     |
|03  |02  |80     |
|03  |03  |80     |
+----+----+-------+


-- 42. 查询每门功成绩最好的前两名。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;

+----+----+-------+
|s_id|c_id|s_score|
+----+----+-------+
|01  |01  |80     |
|03  |01  |80     |
|01  |02  |90     |
|07  |02  |89     |
|01  |03  |99     |
|07  |03  |98     |
+----+----+-------+


-- 43. 统计每门课程的学生选修人数（超过5人的课程才统计）。要求输出课程号和选修人数，查询结果按人数降序排列，若人数相同，按课程号升序排列
select c_id, count(*) as total
from score
GROUP BY c_id
HAVING total > 5
ORDER BY total, c_id asc;

+----+-----+
|c_id|total|
+----+-----+
|01  |6    |
|02  |6    |
|03  |6    |
+----+-----+


-- 44. 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;

+----+---+
|s_id|sel|
+----+---+
|01  |3  |
|02  |3  |
|03  |3  |
|04  |3  |
|05  |2  |
|06  |2  |
|07  |2  |
+----+---+


-- 45. 查询选修了全部课程的学生信息
select *
from student
where s_id in (select s_id from score GROUP BY s_id HAVING count(*) = (select count(*) from course));

+----+------+----------+-----+
|s_id|s_name|s_birth   |s_sex|
+----+------+----------+-----+
|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   |
+----+------+----------+-----+


-- 46. 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;

+----------+---+
|s_birth   |age|
+----------+---+
|1990-01-01|33 |
|1990-12-21|32 |
|1990-05-20|33 |
|1990-08-06|33 |
|1991-12-01|31 |
|1992-03-01|31 |
|1989-07-01|34 |
|1990-01-20|33 |
+----------+---+


-- 47. 查询本周过生日的学生
select *
from student
where WEEK(DATE_FORMAT(NOW(), '%Y%m%d')) = WEEK(s_birth);

select *
from student
where YEARWEEK(s_birth) = YEARWEEK(DATE_FORMAT(NOW(), '%Y%m%d'));

select WEEK(DATE_FORMAT(NOW(), '%Y%m%d'));

-- 48. 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);

-- 49. 查询本月过生日的学生
select *
from student
where MONTH(DATE_FORMAT(NOW(), '%Y%m%d')) = MONTH(s_birth);

-- 50. 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);

+----+------+----------+-----+
|s_id|s_name|s_birth   |s_sex|
+----+------+----------+-----+
|02  |钱电   |1990-12-21|男   |
|05  |周梅   |1991-12-01|女   |
+----+------+----------+-----+