MySQL基础 - MySQL查询、事务、ACID特性

-- 创建SRS数据库

drop database if exists SRS;
create database SRS default charset utf8 collate utf8_bin;

-- 切换到SRS数据库

use SRS;

-- 创建学院表

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)
);

-- 添加唯一约束

alter table tb_college add constraint uni_college_collname unique (collname);

-- 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)
);

-- 添加外键约束

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

-- 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'
);

-- 添加主键约束

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);

-- 创建课程表

create table tb_course
(
couid int not null comment '课程编号',
cname varchar(50) not null comment '课程名称',
credit tinyint not null comment '学分',
teaid int not null comment '教师工号',
primary key (couid)
);

-- 添加外键约束

alter table tb_course add constraint fk_course_tid foreign key (teaid) references tb_teacher (teaid);

-- 创建学生选课表

create table tb_score
(
scid int not null auto_increment comment '选课编号',
sid int not null comment '学号',
cid int not null comment '课程编号',
seldate date comment '选课时间日期',
mark decimal(4,1) comment '考试成绩',
primary key (scid)
);

-- 添加外键约束
维持一对多关系，要在多的一边添加外键约束

alter table tb_score add constraint fk_score_sid foreign key (sid) references tb_student (stuid);
alter table tb_score add constraint fk_score_cid foreign key (cid) references tb_course (couid);

-- 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');

-- 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);

-- 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);

-- 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);

-- 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, date(now()), null),
(3755, 1111, date(now()), null),
(3755, 8888, date(now()), null),
(3755, 9999, '2017-09-01', 92);

-- 查询所有学生的信息

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 as 学分 from tb_course;

-- 查询所有女学生的姓名和出生日期（筛选）

select sname as 姓名, birth as 出生日期 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 as 姓名, if(gender, '男', '女') as 性别, birth as 出生日期
from tb_student where birth between '1980-1-1' and '1989-12-31';

-- 查询姓”杨“的学生姓名和性别(模糊)

select sname as 姓名, if(gender, '男', '女') as 性别 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 as 姓名, case gender when 1 then '男' else '女' end as 性别 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 as 姓名, if(gender, '男', '女') as 性别 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 as 姓名 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)

select sname as 姓名 from tb_student
where addr is null;

-- 查询录入了家庭住址的学生姓名(空值)

select sname as 姓名 from tb_student
where addr is not null;

-- 查询学生选课的所有日期(去重)

select distinct seldate as 选课日期 from tb_score;

-- 查询学生的家庭住址(去重)

select distinct addr as 家庭住址 from tb_student;

-- 查询男学生的姓名和生日按年龄从大到小排列(排序)

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

-- 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;

-- 查询年龄最小的学生的出生日期(聚合函数)

select max(birth) from tb_student;

-- 查询男女学生的人数(分组和聚合函数)

select if(gender, '男', '女') as 性别, count(stuid) as 人数
from tb_student group by gender order by 人数 desc;

-- 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) as 平均成绩 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 avg(mark) as 平均分 from tb_score 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 as 学号,  avg(mark) as 平均成绩 from tb_score group by sid;

-- 查询平均成绩大于等于90分的学生的学号和平均成绩
-- 分组之前的筛选用where，分组之后的筛选用having

select sid as 学号,  avg(mark) as 平均成绩 from tb_score
group by sid having 平均成绩>=90;

-- 子查询 - 在一个查询中又使用到了另外一个查询的结果
-- 查询年龄最大的学生的姓名(子查询)

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 as 姓名, year(now())-year(birth) as 年龄 from tb_student
where birth=(select 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 as 姓名 from tb_student
where stuid in (
select sid from tb_score group by sid having count(sid)>2
);

-- 查询学生的姓名和所在学院的名称
-- 如果查询多个表没有任何限制条件那么将产生笛卡尔积
-- 如果查询的多张表中有同名的列那么需要使用完全限定名

select sname, collname
from tb_student t1, tb_college t2
where t1.collid=t2.collid;

select sname, collname from tb_student t1
inner join tb_college t2
on t1.collid=t2.collid;

-- 连接查询（联结查询/联接查询）
-- 查询学生姓名、课程名称以及成绩

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

select sname, cname, mark from tb_student
inner join tb_score on stuid=sid
inner join tb_course on couid=cid;

-- 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 t1 inner join
(select sid, avg(mark) as avgmark from tb_score group by sid) t2
on stuid=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, coursenum from tb_student t1 left outer join
(select sid, count(sid) as coursenum from tb_score group by sid) t2
on t1.stuid=t2.sid;

-- 事务（transaction):多个操作不可分割要么全成功要么全失败

-- 开启事务:begin;/start transaction;

-- 提交事务:commit;

-- 回滚事务:rollback;

-- 事务的ACID特性：
-- 原子性（Atomicity）：事务中的操作不可分割
-- 一致性（Consistency）：事务前后数据状态要一致
-- 隔离性（Isolation）：多个并发事务不能看到彼此的中间状态
-- 持久性（Duration）：事务完成后数据要持久化

-- 查询薪资最高的员工姓名和工资

select ename as 姓名, sal+if(comm is null, 0, comm) as 薪资 
from tbemp order by 薪资 desc
limit 1;

-- 查询员工的姓名和年薪((月薪+补贴)*12)

select ename as 姓名, (sal*12+if(comm is not null, comm, 0)*12) as 年薪 from tbemp;

-- 查询有员工的部门的编号和人数

select dno, count(dno) as 人数 from tbemp group by dno;

-- 查询所有部门的名称和人数

select dname as 部门, count(tbdept.dno) as 人数
from tbdept, tbemp
where tbemp.dno=tbdept.dno
group by tbemp.dno;

-- 查询薪资最高的员工(Boss除外)的姓名和工资

select ename as 姓名, sal+if(comm is null, 0, comm) as 薪资 
from tbemp
where mgr is not null
order by 薪资 desc
limit 1;

-- 查询薪水超过平均薪水的员工的姓名和工资

select ename as 姓名, sal+if(comm is null, 0, comm) as 薪水 from tbemp
where sal+if(comm is null, 0, comm) >
(select avg(sal+if(comm is null, 0, comm)) from tbemp);

-- 查询主管的姓名和职位

select ename as 姓名, job as 职位 from tbemp where job like "%主管"

-- 查询薪资排名4~6名的员工姓名和工资

select ename as 姓名, sal+if(comm is null, 0, comm) as 薪资 
from tbemp order by 薪资 desc
limit 3,3;