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2021-05-15 21:36:00 阅读：178 来源： 互联网

标签：-- grade score sql cno where select

mysql建表规则和基本使用语法
数据库的设计范式数据库的设计范式

要求：每一个分量必须是不可分的数据项。

特点：

1）有主键，且主键不能为空。

2）字段不能再分。

2.第二范式（2NF）

要求：在范式一的基础上，且每一个非主属性完全函数依赖于主键。

特点：

1）满足第一范式。

2）表中的每一个非主属性，必须完全依赖于本表主键。

3）只有当一个表中，主键由两个或以上的属性组成的时候，才会出现不符合第二范式的情况。(如果出现不完全依赖那么只能发生在联合主键的情况下。

3.第三范式（3NF）

要求：在第二范式的基础上，且消除传递依赖性1）满足第二范式

2）所有的非主键列依赖于主键列

注：3NF是对字段冗余性的约束，即任何字段不能由其他字段派生出来，它要求字段没有冗余，但是没有数据冗余的数据库并不一定是最好的数据库，所以有没有冗余的设计，要综合来考虑

-----mysql的查询语句练习

学生表 student 学号姓名性别出生年月日所在班级
create table student(
sno varchar(20) primary key,
sname varchar(20) not null,
ssex varchar(12) not null,
sbirthday datetime,
cla int(12)
);
insert into student values("101","曾华","男","1977-09-01","95033");
insert into student values("102","匡明","男","1975-10-02","95031");
insert into student values("103","王丽","女","1976-01-23","95033");
insert into student values("105","匡yi明","男","1975-10-02","95031");
insert into student values("104","王er丽","女","1976-01-23","95033");
insert into student values("106","陆君","男","1974-06-03","95031");

--课程表 course 课程号课程名称教师编号
表的约束--外键约束 foreign key reference
1 外键约束
一个表中某字段的值，受另一张表中某个字段的限制
主表（父表）：提供数据的表
从表（子表）：外键所在的表（引用主表中唯一性字段（主健，唯一）的值）
外键的值只能是主表中对应字段的值或者为null
foreign key references 主表(字段) --无名
constraint 约束名 foreign key references 主表(字段) -- 有名
foreign key references 主表(字段)
constraint 约束名 foreign key references 主表(字段)

    create table course(
        cno varchar(20) primary key,
        cname varchar(20) not null,
        tno varchar(20) not null,
        foreign key(tno) references teacher(tno)

);

insert into course values("3-105","计算机导论","825");
insert into course values("6-166","数字电路","856");
insert into course values("9-888","高等数学","831");

教师表 teacher 教师编号教师名字教师性别出生年月日职称所在部门

create table teacher(
tno varchar(20) primary key,
tname varchar(20) not null,
tsex varchar(10) not null,
tbirthday datetime,
prof varchar(20) not null,
depart varchar(20) not null
);
insert into teacher values("804","李诚","男","1958-12-02","副教授","计算机系");
insert into teacher values("856","张旭","男","1969-03-12","讲师","电子工程系");
insert into teacher values("825","王萍","女","1972-05-05","助教","计算机系");
insert into teacher values("831","刘冰","女","1977-08-14","副教授","电子工程系");

– 成绩表
– Score
– 学号
– 课程号
– 成绩
-----------drop table score;
create table score(
sno varchar(20) not null,
cno varchar(20) not null,
grade decimal,
foreign key(sno) references student(sno),
foreign key(cno) references course(cno),
primary key(sno,cno)
);
insert into score values("103","3-105","92");
insert into score values("103","6-166","85");
insert into score values("103","9-888","86");
insert into score values("105","3-105","88");
insert into score values("105","6-166","79");
insert into score values("105","9-888","75");
insert into score values("106","3-105","76");
insert into score values("106","6-166","81");
insert into score values("106","9-888","68");

sql 查询语句
select * from student; 查询student中的所有数据
select sname from student; 查询student中的sname字段的值
select distinct depart from teacher; 查询教师所有的单位既不重复的depart的值 -- distinct 去重
-- 查询score表中的成绩在60-80的所有记录。
-- 查询区间 between...and
select * from score where 60<grade<80;
select * from score where grade between 60 and 80;
-- 查询 score 表中成绩为85，86或88的纪录。
-- 表示或者的关系查询 in
select * from score where grade in(85,86,88);
mysql> select * from score where grade in(85,86,88);
+-----+-------+-------+
| sno | cno | grade |
+-----+-------+-------+
| 103 | 6-166 | 85 |
| 103 | 9-888 | 86 |
| 105 | 3-105 | 88 |
+-----+-------+-------+
3 rows in set (0.00 sec)

-- 查询student表中'96031'班或性别为女的同学纪录
-- or表示或者
select * from student where class='95031' or ssex='女';
-- 以cla降序查询student表中的所有记录。
-- 升序order by asc 降序 order by desc
select * from student order by cla desc;
-- 以cno升序，degree降序查询score 表中的所有记录
select * from score order by cno asc,grade desc;
mysql> select * from score order by cno asc,grade desc;
+-----+-------+-------+
| sno | cno | grade |
+-----+-------+-------+
| 103 | 3-105 | 92 |
| 105 | 3-105 | 88 |
| 106 | 3-105 | 76 |
| 103 | 6-166 | 85 |
| 106 | 6-166 | 81 |
| 105 | 6-166 | 79 |
| 103 | 9-888 | 86 |
| 105 | 9-888 | 75 |
| 106 | 9-888 | 68 |
+-----+-------+-------+
9 rows in set (0.00 sec)
-- 查询'95031'班的学生人数。
-- 统计count
select count() from student where cla='95031';
mysql> select count() from student where cla='95031';
+----------+
| count(*) |
+----------+
| 3 |
+----------+
1 row in set (0.00 sec)

-- 查询score表中的最高分的学生学号和课程号。（子查询或者排序）
-- 分析：找到最高分 select max(grade) from score;
-- 找到最高分的sno,cno
select sno,cno from score where grade=(select max(grade) from score);
-- 排序分析：limit 0,1 0表示开始索引,1表示取几个
-- select sno,cno,grade from score order by grade;
-- select sno,cno,grade from score order by grade desc limit 0,1;
mysql> select sno,cno from score where grade=(select max(grade) from score);
+-----+-------+
| sno | cno |
+-----+-------+
| 103 | 3-105 |
+-----+-------+
1 row in set (0.00 sec)

-- 查询每门课的平均成绩
-- avg(grade)
select avg(grade) from score where cno='9-888';
mysql> select avg(grade) from score where cno='9-888';
+------------+
| avg(grade) |
+------------+
| 76.3333 |
+------------+
1 row in set (0.00 sec)
-- 查询每门课
-- group by 分组
select cno,avg(grade) from score group by cno;
mysql> select cno,avg(grade) from score group by cno;
+-------+------------+
| cno | avg(grade) |
+-------+------------+
| 3-105 | 85.3333 |
| 6-166 | 81.6667 |
| 9-888 | 76.3333 |
+-------+------------+
3 rows in set (0.00 sec)

-- 查询score表中至少有2名学生选修的并以3开头的平均分数
-- where、聚合函数、having 在from后面的执行顺序：
-- where>聚合函数(sum,min,max,avg,count)>having
-- having条件若须引入聚合函数来对group by 结果进行过滤则只能用having
-- like 模糊查询类似正则
-- 分析：先分组 select cno,avg(grade) from score group by cno
-- 第二步 having count(2)>=2
-- 第三步 and cno like '3%';
select cno,avg(grade),count(*) from score group by cno having count(cno)>=2 and cno like '3%';

注意：
1、where 后不能跟聚合函数，因为where执行顺序大于聚合函数。
2、where 子句的作用是在对查询结果进行分组前，将不符合where条件的行去掉，即在分组之前过滤数据，条件中不能包含聚组函数，使用where条件显示特定的行。
3、having 子句的作用是筛选满足条件的组，即在分组之后过滤数据，条件中经常包含聚组函数，使用having 条件显示特定的组，也可以使用多个分组标准进行分组。

-- 查询分数大于70，小于90的sno列。
select sno grade from score where 70<grade<90;
select sno grade from score where grade between 70 and 90;

-- 查询所有学生的sname,cno 和grade列
select sname,cno,grade from student as st,score as sc where st.sno=sc.sno;
mysql> select sname,cno,grade from student as st,score as sc where st.sno=sc.sno;
+--------+-------+-------+
| sname | cno | grade |
+--------+-------+-------+
| 王丽 | 3-105 | 92 |
| 王丽 | 6-166 | 85 |
| 王丽 | 9-888 | 86 |
| 匡yi明 | 3-105 | 88 |
| 匡yi明 | 6-166 | 79 |
| 匡yi明 | 9-888 | 75 |
| 陆君 | 3-105 | 76 |
| 陆君 | 6-166 | 81 |
| 陆君 | 9-888 | 68 |
+--------+-------+-------+
9 rows in set (0.00 sec)

-- 查询所有学生的sno，cname和grade列 course cname score sno and grade
select sno,cname,grade from course as c,score as s where c.cno=s.cno;
mysql> select sno,cname,grade from course as c,score as s where c.cno=s.cno;
+-----+------------+-------+
| sno | cname | grade |
+-----+------------+-------+
| 103 | 计算机导论 | 92 |
| 103 | 数字电路 | 85 |
| 103 | 高等数学 | 86 |
| 105 | 计算机导论 | 88 |
| 105 | 数字电路 | 79 |
| 105 | 高等数学 | 75 |
| 106 | 计算机导论 | 76 |
| 106 | 数字电路 | 81 |
| 106 | 高等数学 | 68 |
+-----+------------+-------+
9 rows in set (0.00 sec)

-- 查询所有学生的sname，cname和grade列
-- sname--student cname--course grade--score
select sname,cname,grade from student as st,course as c,score as sc where c.cno=sc.cno and st.sno=sc.sno;
mysql> select sname,cname,grade from student as st,course as c,s
c.cno=sc.cno and st.sno=sc.sno;
+--------+------------+-------+
| sname | cname | grade |
+--------+------------+-------+
| 王丽 | 计算机导论 | 92 |
| 王丽 | 数字电路 | 85 |
| 王丽 | 高等数学 | 86 |
| 匡yi明 | 计算机导论 | 88 |
| 匡yi明 | 数字电路 | 79 |
| 匡yi明 | 高等数学 | 75 |
| 陆君 | 计算机导论 | 76 |
| 陆君 | 数字电路 | 81 |
| 陆君 | 高等数学 | 68 |
+--------+------------+-------+
9 rows in set (0.00 sec)

-- 查询95031班的学生每门课的平均分数 avg()平均分时
-- in 表示或的关系
-- cla-95031--student表 grade--score表课程名称 cname--course
select avg(grade),cno from score where sno in (select sno from student where cla='95031') group by cno;
select cla,avg(grade),cname from student as st,course as co,score as sc where st.sno=sc.sno and co.cno=sc.cno;

-- 查询选修3-105课程的成绩高于106号同学3-105成绩的所有同学的记录
select grade from score where sno='106' and cno='3-105';
select * from score where cno='3-105' and grade>(select grade from score where sno='106' and cno='3-105');
mysql> select * from score where cno='3-105' and grade>(select grade from score
where sno='106' and cno='3-105');
+-----+-------+-------+
| sno | cno | grade |
+-----+-------+-------+
| 103 | 3-105 | 92 |
| 105 | 3-105 | 88 |
+-----+-------+-------+
2 rows in set (0.00 sec)

-- 查询成绩高于学号106课程为3-105的成绩的所有记录
select * from score where grade>(select grade from score where sno='106' and cno='3-105');

-- 查询学号为108,101的同学同年出生的所有学生的sno，sname和sbirthday列。
-- 只要查年份 year(sbirthday)
select * from student where year(sbirthday) in (select year(sbirthday) from student where sno in (101,103));

-- 查询张旭教师任课的学生成绩。
select * from teacher where tname ='张旭';
select cno from course where tno=(select * from teacher where tname ='张旭');

-- 查询选修某课程的同学人数多于3人的教师姓名
select cno from score group by cno having count()>2;
select tname from teacher where tno=(select tno from course where cno=(select cno from score group by cno having count()>3));

-- 查询95033班和95031班的全体学生的记录
select * from student where cla in ('95033','95031');

-- 查询存在有85分以上成绩的课程cno.
select cno from score where grade>85;

-- 查询出计算机系教师所教课程的成绩表。
select * from score where cno in (select cno from course where tno in (select tno from teacher where depart="计算机系"));

-- 查询计算机系和电子工程系不同职称的教师的tname和prof。
-- union 求并集
select prof from teacher where depart='电子工程系';
select * from teacher where depart='计算机系' and prof not in(select prof from teacher where depart='电子工程系')
union
select * from teacher where depart='电子工程系' and prof not in(select prof from teacher where depart='计算机系');

mysql> select * from teacher where depart='计算机系' and prof not in(select pro
from teacher where depart='电子工程系')
-> union
-> select * from teacher where depart='电子工程系' and prof not in(select
rof from teacher where depart='计算机系');
+-----+-------+------+---------------------+------+------------+
| tno | tname | tsex | tbirthday | prof | depart |
+-----+-------+------+---------------------+------+------------+
| 825 | 王萍 | 女 | 1972-05-05 00:00:00 | 助教 | 计算机系 |
| 856 | 张旭 | 男 | 1969-03-12 00:00:00 | 讲师 | 电子工程系
|
+-----+-------+------+---------------------+------+------------+
2 rows in set (0.00 sec)

-- 查询选修编号为3-105课程且成绩至少高于选修编号为3-166的同学的cno，sno和grade,且成绩从高到低次序排列。
-- any 大于其中至少一个
select * from score where cno='6-166';
select * from score where cno='3-105';
select * from score where cno='3-105' and grade>any(select grade from score where cno='6-166')
order by grade desc;

-- 查询选修编号为3-105课程且成绩至少高于选修编号为3-166的同学的cno，sno和grade
-- all 表示所有

select * from score where cno='6-166';
select * from score where cno='3-105';
select * from score where cno='3-105' and grade>all(select grade from score where cno='6-166');

-- 查询所有教师和同学的name，sex和birthday.
select tname,tsex,tbirthday from teacher
union
select sname,ssex,sbirthday from student;

-- 查询所有女教师和女同学的name，sex和birthday
select tname,tsex,tbirthday from teacher where tsex='女'
union
select sname,ssex,sbirthday from student where ssex='女';

-- 查询成绩比该课程平均成绩低的同学的成绩表。
-- 复制表score为表a和表b
select con,avg(grade) from score group by cno;
select * from score a where grade<(select avg(grade) from score b where a.cno = b.cno);
mysql> select * from score a where grade<(select avg(grade) from score b where
a.cno = b.cno);
+-----+-------+-------+
| sno | cno | grade |
+-----+-------+-------+
| 105 | 6-166 | 79 |
| 105 | 9-888 | 75 |
| 106 | 3-105 | 76 |
| 106 | 6-166 | 81 |
| 106 | 9-888 | 68 |
+-----+-------+-------+
5 rows in set (0.00 sec)

-- 查询所有任课教师的tname和depart
select tname,depart from teacher where tno in (select tno from course);

-- 查询至少有俩名男生的班号。
select cla from student where ssex='男' group by cla having count(*)>1;

-- 查询student表中不性王的同学记录。
select * from student;
select * from student where sname not like '王%';

-- 查询student表中每个学生的姓名和年龄
-- year(now()) 查看当前年份
select sname,year(now())-year(sbirthday) from student;

-- 查询student表中最大值和最小的birthday的日期值
select max(sbirthday) as '最大值',min(sbirthday) as '最小值' from student;
mysql> select max(sbirthday) as '最大值',min(sbirthday) as '最小值' from student
;
+---------------------+---------------------+
| 最大值 | 最小值 |
+---------------------+---------------------+
| 1977-09-01 00:00:00 | 1974-06-03 00:00:00 |
+---------------------+---------------------+
1 row in set (0.00 sec)

-- 以班号和年龄从大到小的顺序查询studente表中的全部记录。
select * from student order by cla desc,sbirthday;

-- 查询男教师及其所上的课程
select * from course where tno in (select tno from teacher where tsex='男');

-- 查询最高分同学的sno,cno,和grade.
select * from score where grade=(select max(grade) from score);

-- 查询和王丽同性别的所有同学的sname
select ssex from student where sname='王丽';
select sname from student where ssex=(select ssex from student where sname='王丽');

-- 查询和王丽同性别并在同班的同学sname
select ssex from student where sname='王丽';
select sname from student where ssex=(select ssex from student where sname='王丽') and cla=(select cla from student where sname='王丽');

-- 查询所有选修计算机导论课程的男同学的成绩表。
select * from student where ssex='男';
select * from course where cname='计算机导论';
select * from score where cno=(select cno from course where cname='计算机导论') and sno in (select sno from student where ssex='男');

-- 假设用如下命令建立了一个grade表
create table gradeq(
low int(3),
upp int(3),
gradet char(1)
);
insert into gradeq values(90,100,'A');
insert into gradeq values(80,90,'B');
insert into gradeq values(70,80,'C');
insert into gradeq values(60,70,'D');
insert into gradeq values(50,60,'E');
-- 先查询所有学生的sno cno 和 gradet列
select sno,cno,gradet from score,gradeq where grade between low and upp;
mysql> select sno,cno,gradet from score,gradeq where grade between low and upp;
+-----+-------+--------+
| sno | cno | gradet |
+-----+-------+--------+
| 101 | 3-105 | A |
| 103 | 3-105 | A |
| 103 | 6-166 | B |
| 103 | 9-888 | B |
| 105 | 3-105 | B |
| 105 | 6-166 | C |
| 105 | 9-888 | C |
| 106 | 3-105 | C |
| 106 | 6-166 | B |
| 106 | 9-888 | D |
+-----+-------+--------+
10 rows in set (0.00 sec)
sql 的四种连接查询
-- 内连接 inner join 或者 join
-- 外连接
-- 左连接 left join 或者 left outer join
-- 有连接 right join 或者 right outer join
-- 完全外连接 full 或者 full outer join

创建俩个表
person表 id,name,cardId
create table person(
id int,
name varchar(20),
cardId int
);
insert into person values(1,'张三',1);
insert into person values(2,'李四',3);
insert into person values(3,'王五',6);
insert into person values(4,'马六',9);

card表 id,name
create table card(
id int,
name varchar(20)
);

insert into card values(1,'饭卡');
insert into card values(2,'中国卡');
insert into card values(3,'交通卡');
insert into card values(4,'招商卡');
insert into card values(5,'平安卡');

-- 并没有创建外键
-- inner join 查询(内连接) 或者可以使用join
-- 代码解析：俩张表连接以后使得cardId=id使用inner join 来连接
-- join 左右是我们关联的表后跟on 后面的是条件
select * from person inner join card on person.cardId=card.id;
mysql> select * from person inner join card on person.cardId=card.id;
+------+------+--------+------+--------+
| id | name | cardId | id | name |
+------+------+--------+------+--------+
| 1 | 张三 | 1 | 1 | 饭卡 |
| 2 | 李四 | 3 | 3 | 交通卡 |
+------+------+--------+------+--------+
2 rows in set (0.00 sec)

-- left join 外连接（左连接）或者 left outer join
select * from person left join card on person.cardId=card.id;
mysql> select * from person left join card on person.cardId=card.id;
+------+------+--------+------+--------+
| id | name | cardId | id | name |
+------+------+--------+------+--------+
| 1 | 张三 | 1 | 1 | 饭卡 |
| 2 | 李四 | 3 | 3 | 交通卡 |
| 3 | 王五 | 6 | NULL | NULL |
| 4 | 马六 | 9 | NULL | NULL |
+------+------+--------+------+--------+
4 rows in set (0.00 sec)
-- 左外连接,会把左面的数据全都拿出来，而又变得数据条件相等的拿，不等的补NULL

-- right join 外连接(右链接) 或者 right outer join
select * from person right join card on person.cardId=card.id;
mysql> select * from person right join card on person.cardId=card.id;
+------+------+--------+------+--------+
| id | name | cardId | id | name |
+------+------+--------+------+--------+
| 1 | 张三 | 1 | 1 | 饭卡 |
| NULL | NULL | NULL | 2 | 中国卡 |
| 2 | 李四 | 3 | 3 | 交通卡 |
| NULL | NULL | NULL | 4 | 招商卡 |
| NULL | NULL | NULL | 5 | 平安卡 |
+------+------+--------+------+--------+
5 rows in set (0.00 sec)
-- 右外连接,会把右面的数据全都拿出来，而又变得数据条件相等的拿，不等的补NULL

-- full join 全外连接
----------- mysql 不支持 full join 外连接 ---------
select * from person full join card on person.cardId=card.id;
-- 所以mysql如果需要实现全外连接就需要用左连接union有链接即可
select * from person right join card on person.cardId=card.id
union
select * from person left join card on person.cardId=card.id;
mysql> select * from person right join card on person.cardId=card.id
-> union
-> select * from person left join card on person.cardId=card.id;
+------+------+--------+------+--------+
| id | name | cardId | id | name |
+------+------+--------+------+--------+
| 1 | 张三 | 1 | 1 | 饭卡 |
| NULL | NULL | NULL | 2 | 中国卡 |
| 2 | 李四 | 3 | 3 | 交通卡 |
| NULL | NULL | NULL | 4 | 招商卡 |
| NULL | NULL | NULL | 5 | 平安卡 |
| 3 | 王五 | 6 | NULL | NULL |
| 4 | 马六 | 9 | NULL | NULL |
+------+------+--------+------+--------+
7 rows in set (0.00 sec)

数据库的设计范式