sql基本语句

structured query language(结构化查询语言)

root

测试mysql是否安装成功：
mysql -uroot -p
show databases;

创建一个名称为mydb1的数据库。
mysql -uroot -p
create database mydb1;
show databases;

创建一个使用utf-8字符集的mydb2数据库。
create database mydb2 character set utf8;

创建一个使用utf-8字符集，并带校对规则的mydb3数据库。
create database mydb3 character set utf8 collate utf8_general_ci;

查看前面创建的mydb2数据库的定义信息
show create database mydb2;

删除前面创建的mydb1数据库
drop database mydb1;

查看服务器中的数据库，并把其中mydb2的字符集修改为gb2312;
alter database mydb2 character set gb2312;
show create database mydb2;


数据库的备份和恢复

1.准备数据
create database mydb4;
use mydb4;
create table test
(
id int
);
insert into test(id) values(1);

quit;

2、备份库
mysqldump -uroot -proot mydb4>d:\1.sql

3、删除库
mysql -uroot -proot
drop database mydb4;
4、恢复库
create database mydb4;
quit
mysql -uroot -proot mydb4source d:\1.sql


创建带时间戳的表
create table test2
(
name varchar(20),
time TimeStamp
);

创建一个员工表
进入库：use mydb2
create table employee
(
id int,
name varchar(40),
gender varchar(10),
birthday date,
entry_date date,
job varchar(100),
salary double,
resume text
)character set utf8;

在上面员工表的基本上增加一个image列。
alter table employee add image blob;

修改job列，使其长度为60。
alter table employee modify job varchar(60);

删除sex列。
alter table employee drop gender;

看修改后的结果
show create table employee;(看表的创建语法)
desc employee (看表的结构)

表名改为user。
rename table employee to user;

修改表的字符集为utf-8
alter table user character set utf8;

列名name修改为username
alter table user change column name username varchar(40);

删除表
drop table user;


使用insert语句向employee表中插入一个员工的信息。
rename table user to employee;
insert into employee(id,username,birthday,entry_date,job,salary,resume) values(1,'aaa','1980-09-09','1989-09-09','aaa',98.98,'aaaaa');


使用insert语句插入中文数据
show variables like 'character%'; (显示mysql中所有涉及到字符编码的变量)
set character_set_client=gb2312;

insert into employee(id,username,birthday,entry_date,job,salary,resume) values(2,'李一','1980-09-09','1989-09-09','aaa',98.98,'aaaaa');

显示中文数据
set character_set_results=gb2312;
select * from employee;


将所有员工薪水修改为5000元。
update employee set salary=5000;
select * from employee;

将姓名为aaa’的员工薪水修改为3000元。
update employee set salary=3000 where username='aaa';

将姓名为’aaa’的员工薪水修改为4000元,job改为ccc。
updat

e employee set salary=4000,job='ccc' where username='aaa';

将aaa的薪水在原有基础上增加1000元。
update employee set salary=salary+1000 where username='aaa';

删除表中名称为’zs’的记录。
delete from employee where username='aaa';

删除表中所有记录
delete from employee;

使用truncate删除表中记录
truncate table employee;

查询表中所有学生的信息。
select * from student
select id,name,chinese,english,math from student;

查询表中所有学生的姓名和对应的英语成绩。
select name,english from student;

过滤表中重复的英语成绩
select distinct name,english from student;

在所有学生每课成绩上加10分。
select name,(chinese+10),english+10,math+10 from student;

统计每个学生的总分。
select name,(chinese+english+math) from student;

使用别名表示学生分数。
select name as 姓名,(chinese+english+math) as 总分 from student;

查询姓名为wu的学生成绩
select * from student where name='wu';

查询英语成绩大于90分的同学
select * from student where english>90;

查询总分大于200分的所有同学
select * from student where (math+english+chinese)>200;

查询英语分数在 80－90之间的同学。
select * from student where english>=80 and english<=90;
select * from student where english between 80 and 90;

查询数学分数为89,90,91的同学。
select * from student where math in(89,90,91);
select * from student where math=89 or math=90 or math=91;

查询所有姓李的学生成绩。
select * from student where name like '李%';

查询数学分>80，语文分>80的同学。
select * from student where math>80 and chinese>90;

对数学成绩排序后输出。
select name,math from student order by math;

对总分排序后输出，然后再按从高到低的顺序输出
select name from student order by(english+math+chinese) desc;

对姓李的学生成绩排序输出
select name from student where name like '李%' order by(english+math+chinese) desc;

统计一个班级共有多少学生？
select count(*) from student;

统计数学成绩大于90的学生有多少个？
select count(*) from student where math>90;

统计总分大于250的人数有多少？
select count(*) from student where (math+chinese+english)>250;

统计一个班级数学总成绩？
select sum(math) from student;

统计一个班级语文、英语、数学各科的总成绩
select sum(chinese),sum(english),sum(math) from student;

统计一个班级语文、英语、数学的成绩总和
select sum(chinese+english+math) from student;

统计一个班级语文成绩平均分
select sum(chinese)/count(chinese) from student;

求一个班级数学平均分？
select avg(math) from student;

求一个班级总分平均分
select avg(math+chinese+english) from student;

求班级最高分和最低分
select max(math+chinese+english),min(math+chinese+english) fr

om student;

请统计表中共有几种商品
select product from orders group by(product);

对商品归类后，统计每一类商品花了多少钱
select product,sum(price) from orders group by(product);

查询购买了几类商品，并且每类总价大于100的商品
select product from orders group by(product) where sum(price)>100;
select product,sum(price) from orders group by(product) having sum(price)>100;


定义主键约束
create table person
(
id int primary key,
name varchar(40)
);

定义主键自动增长
create table person2
(
id int primary key auto_increment,
name varchar(40)
);

定义唯一约束
create table person3
(
id int primary key auto_increment,
name varchar(40) unique
);

定义非空约束
create table person4
(
id int primary key auto_increment,
name varchar(40) unique not null
);

定义外键约束
create table husband
(
id int primary key,
name varchar(40)
);

create table wife
(
id int primary key,
name varchar(40),
husband_id int,
constraint husband_id_FK foreign key(husband_id) references husband(id)
);


部门关系管理
create table department
(
id int primary key,
name varchar(40) not null unique
);

create table employee
(
id int primary key,
name varchar(40) not null unique,
salary double not null,
department_id int,
constraint department_id_FK foreign key(department_id) references department(id)
);


老师和学生
create table teacher
(
id int primary key,
name varchar(40) not null unique,
salary double not null
);

create table student
(
id int primary key,
name varchar(40) not null unique
);

create table teacher_student
(
teacher_id int,
student_id int,
primary key(teacher_id,student_id),
constraint teacher_id_FK foreign key(teacher_id) references teacher(id),
constraint student_id_FK foreign key(student_id) references student(id)
);


身份证管理系统(一对一的关系)
create table person
(
id int primary key,
name varchar(40)
);

create table idcard
(
id int primary key,
address varchar(100),
constraint id_FK foreign key(id) references person(id)
);


查询出1号老师所有的学生
select from teacher_student ts,student s where ts.teacher_id=1 and ts.student_id=s.id;


找出开发部所有的员工

insert into employee(id,name,salary,department_id) values(1,'aa',100,1);
insert into employee(id,name,salary,department_id) values(2,'bb',100,1);
insert into employee(id,name,salary,department_id) values(3,'cc',100,2);

select from department d,employee e where ='kafa' and d.id=e.department_id;