数据库操作-建表 | lorry

sql

MySql 2018-12-26

1.创建数据库

– 如果存在srs的数据库就删除它（慎重），之后创建数据库并且进入数据库。

drop database if exists srs;
create database srs default charset utf8;
use srs;

2.创建二维表

例子：创建学生管理表并且添加信息

1.创建学员表

create table tb_college
(
collid int not null auto_increment comment '学院编号',
collname varchar(50) not null comment '学院名称',
collmaster varchar(20) not null comment '院长姓名',
collweb varchar(511) default '' comment '学院网站',
primary key (collid)
);

添加唯一性约束到学院名称

alter table tb_college add constraint uni_college_collname unique (collname);

2.创建学生表

create table tb_student
(
stuid int not null comment '学号',
sname varchar(20) not null comment '学生姓名',
gender bit default 1 comment '性别',
birth date not null comment '出生日期',
addr varchar(255) default '' comment '籍贯',
collid int not null comment '所属学院编号',
primary key (stuid)
);

检查约束，mysql不支持：

alter table tb_student add constraint ck_student_birth check (birth between '1990-1-1' and '1999-12-31');

添加外键约束

alter table tb_student add constraint fk_student_collid foreign key (collid) references tb_college (collid);

3.创建教师表

create table tb_teacher
(
teaid int not null comment '教师工号',
tname varchar(20) not null comment '教师姓名',
title varchar(10) default '' comment '职称',
collid int not null comment '所属学院编号'
);

添加外键约束

alter table tb_teacher add constraint pk_teacher primary key (teaid);

添加外键约束

alter table tb_teacher add constraint fk_teacher_collid foreign key (collid) references tb_college (collid);

4.插入学院数据

插入学院数据
`
insert into tb_college (collname, collmaster, collweb) values
(‘计算机学院’, ‘左冷禅’, ‘http://www.abc.com

‘),
(‘外国语学院’, ‘岳不群’, ‘http://www.xyz.com

‘),
(‘经济管理学院’, ‘风清扬’, ‘http://www.foo.com

‘);

#### 5.插入学生数据

insert into tb_student (stuid, sname, gender, birth, addr, collid) values
(1001, ‘杨逍’, 1, ‘1990-3-4’, ‘四川成都’, 1),
(1002, ‘任我行’, 1, ‘1992-2-2’, ‘湖南长沙’, 1),
(1033, ‘王语嫣’, 0, ‘1989-12-3’, ‘四川成都’, 1),
(1572, ‘岳不群’, 1, ‘1993-7-19’, ‘陕西咸阳’, 1),
(1378, ‘纪嫣然’, 0, ‘1995-8-12’, ‘四川绵阳’, 1),
(1954, ‘林平之’, 1, ‘1994-9-20’, ‘福建莆田’, 1),
(2035, ‘东方不败’, 1, ‘1988-6-30’, null, 2),
(3011, ‘林震南’, 1, ‘1985-12-12’, ‘福建莆田’, 3),
(3755, ‘项少龙’, 1, ‘1993-1-25’, null, 3),
(3923, ‘杨不悔’, 0, ‘1985-4-17’, ‘四川成都’, 3);

#### 6.插入老师数据

insert into tb_teacher (teaid, tname, title, collid) values
(1122, ‘张三丰’, ‘教授’, 1),
(1133, ‘宋远桥’, ‘副教授’, 1),
(1144, ‘杨逍’, ‘副教授’, 1),
(2255, ‘范遥’, ‘副教授’, 2),
(3366, ‘韦一笑’, ‘讲师’, 3);

#### 7. 插入课程数据

insert into tb_course (couid, cname, credit, teaid) values
(1111, ‘Python程序设计’, 3, 1122),
(2222, ‘Web前端开发’, 2, 1122),
(3333, ‘操作系统’, 4, 1122),
(4444, ‘计算机网络’, 2, 1133),
(5555, ‘编译原理’, 4, 1144),
(6666, ‘算法和数据结构’, 3, 1144),
(7777, ‘经贸法语’, 3, 2255),
(8888, ‘成本会计’, 2, 3366),
(9999, ‘审计学’, 3, 3366);

#### 8.插入选课数据

insert into tb_score (sid, cid, seldate, mark) values
(1001, 1111, ‘2017-09-01’, 95),
(1001, 2222, ‘2017-09-01’, 87.5),
(1001, 3333, ‘2017-09-01’, 100),
(1001, 4444, ‘2018-09-03’, null),
(1001, 6666, ‘2017-09-02’, 100),
(1002, 1111, ‘2017-09-03’, 65),
(1002, 5555, ‘2017-09-01’, 42),
(1033, 1111, ‘2017-09-03’, 92.5),
(1033, 4444, ‘2017-09-01’, 78),
(1033, 5555, ‘2017-09-01’, 82.5),
(1572, 1111, ‘2017-09-02’, 78),
(1378, 1111, ‘2017-09-05’, 82),
(1378, 7777, ‘2017-09-02’, 65.5),
(2035, 7777, ‘2018-09-03’, 88),
(2035, 9999, curdate(now()), null),
(3755, 1111, date(now()), null),
(3755, 8888, date(now()), null),
(3755, 9999, ‘2017-09-01’, 92);

### 相关sql语句练习
-- **总结** 分组之前的筛选用where子句，分组之后的子句筛选用having。
  - 查询所有学生信息

select * from tb-student;

  - 查询所有课程名称及学分(投影和别名)

select cname as 课程名称,credit from tb_corse

  - 查询所有女学生的姓名和出生日期(筛选)

select sname,birth from tb_student where gender=0;

  - 查询所有80后学生的姓名、性别和出生日期(筛选)

select sname,case gender when 1 then ‘男’ when 2 then ‘女’ else then ‘未知’,birth where birth between ‘1980-1-1 ‘ and ‘1989-12-31’;

  - 查询所有80后学生的姓名、性别和出生日期(筛选)，使用mysql中的分支函数

select sname,if(gender,’男’,’女’),birth where birth between ‘1980-1-1 ‘ and ‘1989-12-31’;

  - 查询名字有四个中文字符字符的学生学号和姓名,一个中文三个字节

select stuid,sname from tb_student where length(sname)/3=4;

  - 查询姓”杨“的学生姓名和性别(模糊)

select sname,if(gender,’男’,’女’) from tb_student where sname like ‘杨%’

  - 查询姓”杨“名字两个字的学生姓名和性别(模糊)

select sname,if(gender,’男’,’女’) from tb_student where sname like ‘杨_’

  - 查询姓”杨“名字三个字的学生姓名和性别(模糊)

select sname,if(gender,’男’,’女’) from tb_student where sname like ‘杨__’

  - 查询名字中有”不“字或“嫣”字的学生的姓名(模糊)

select sname from tb)student where sname like ‘%不%’ or sname like ‘%嫣%’

  - 查询没有录入家庭住址的学生姓名(空值)  更加的严谨

select sname from tb_student where addr is null or addr=’’;

  - 查询录入了家庭住址的学生姓名(空值) 摩根定律

select sname from tb_student where addr is not null or addr<>’’;

  - 查询学生选课的所有日期(去重)-- distinct

select distinct seldate from tb_score

  - 查询学生的家庭住址(去重)

select distinct addr from tb_student where addr is not null and addr<>””;

  - 查询男学生的姓名和生日按年龄从大到小排列(排序)-- 升序   asc 默认

select sname,birth from tb_student where gender=1 order by birth;
select sname,birth from tb_student where gender=1 order by birth desc;
select sname,year(now())-year(birth) as 年龄 from tb_student where gender=1 order by 年龄 asc;

  - 聚合函数 max min sum avg count
  - 查询年龄最大的学生的出生日期(聚合函数)

select min(birth) from tb_student;

selecr sname,birth from tb_student where birth=(select min(birth) from tb_student)

  - 查询男女学生的人数(分组和聚合函数)

select gender,count(gender) from tb_student group by gender;

  - 查询课程编号为1111的课程的平均成绩(筛选和聚合函数)

select avg(mark) from tb_score where cid=1111;

  - 查询学号为1001的学生所有课程的平均分(筛选和聚合函数)

select sid,avg(mark) from tb_sscore where sid=1001;

  - 查询每个学生的学号和平均成绩(分组和聚合函数)

select sid,avg(mark) from tb_score group by sid;

  - 查询平均成绩大于等于90分的且学号为1,2,3开头的学生的学号和平均成绩

select sid,avg(mark) as 平均分 from tb_score where 平均分>90 and sid between 1000 and 3999 order by 平均分 desc;

  - 查询年龄最大的学生的姓名(子查询) 把一个查询的结果当做另一个查询的一部分来使用

select sname from tb_student where birth=(select min(birth) from tb_student);

  - 查询年龄最大的学生姓名和年龄(子查询+运算)

select sname,year(now())-year(birth) from tb_student where birth=(selct min(birth) from tb_student);

  - 查询选了两门以上的课程的学生姓名(子查询/分组条件/集合运算)

select sname from tb_student where stuid in(select sid from tb_score group by sid having count(sid)>2)

  - 查询学生姓名、课程名称以及成绩(链接查询) 链接查询时，如果不使用链接条件，将会产生笛卡尔积

三表联查
select sname,cname,mark from tb_student inner join tb_score on sid=stuid inner jion tb_course on couid=cid limit 5 offset 15;

select sname,cname,mark from tb_student,tb_course,tb_score where stuid=sid and couid=cid order by sname,mark desc;

  - 查询选课学生的姓名和平均成绩(子查询和连接查询)

select sname,avgmark from tb_student as t1 inner join
(select sid,avg(mark) as avgmark from tb_score group by sid) as t2 where t1.stuid=t2.sid;

  - 查询每个学生的姓名和选课数量(左外连接和子查询)

select sname,ifnull(total,0),ifnull(avgmark,0) from tb_student as t1 left join (select sid,count(sid) as total,avg(mark) as avgmark from tb_score group by sid) as t2 on stuid=sid order by total
`
(左表：多表查询时，写在前面的表称为左表left outer join，right outer join ，mysql不支持全外连接：full outer join
– 左外连接，将左表不满足连接条件的记录也要查出来，不满足链表条件的的地方补null
– 右外连接，将右表不满足连接条件的记录也要查出来，不满足链表条件的的地方补null
– 内连接只能将满足条件的表链接起来，不满足的链接条件的不能查出)

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