11:33 2013/6/26
SQL语句:
DML(Data Manipulation Language 数据操作语言)语句：insert update delete select

DDL(Data Difinition Language 数据定义语言)语句：create table/ create database/ drop database/ alter table 
                
DCL(Data Control Language 数据控制语句)语句:

主键可以定义为自动增长
create table d(
    id int primary key auto_increment,
    name varchar(20)
);

insert into d(name) values(‘ccc‘);

insert into d(name) values(‘aaaa‘);

delete from d where id=4;


create table e(
    id int,
    name varchar(20)
);
// 增加主键约束
alter table e modify id int primary key auto_increment;

// 创建联合主键
create table f(
    firstname varchar(20),
    lastname varchar(20),
    primary key(firstname, lastname)
);

insert into f values(‘zhao‘,‘nan‘);
insert into f values(‘li‘, ‘nan‘);


最重要的约束  外键约束
create table husband(
    id int primary key,
    name varchar(20)
);

create table wife(
    id int primary key auto_increment,
    name varchar(20),
    husbandid int,
    constraint husbandid_FK foreign key(husbandid) references husband(id)
);

insert into husband (id,name) values(3,‘liuxiaoshuai‘);

insert into wife (name, husbandid) values(‘fengjie‘, 3);

delete from husband where id=3;

create table aaa(
    id int

);

// 为aaa 加外键约束
alter table aaa add constraint husid_FK foreign key(husid) references husband(id);

// 删除外键约束
alter table aaa drop foreign key husid_FK;

2. 修改表
在上面员工表的基础上增加一个image列
alter table employee add image varchar(30);

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 sex;

表名改为users。
rename table employee to users;

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(20);

查看所有表
show tables;

查看表的创建语句
show create table user;

查看表结构
desc user;

删除 user 表
drop table user;


三、数据的增删改查
1. insert语句
employee.sql
create table employee
(
    id int,
    name varchar(20),
    sex varchar(10),
    birthday date,
    salary float,
    entry_date date,
    resume text
);
create table employee 
(
    id int,
    name varchar(20),
    sex varchar(10),
    birthday date,
    salary float,
    entry_date date,
    resume text
);
// 向员工表插入三条记录
insert into employee(id,name,sex,birthday,salary,entry_date,resume) values(1,‘zjx‘,‘male‘,‘1991-10-08‘,9500,‘2010-2-18‘,‘good boy‘);
insert into employee(id,name,sex,birthday,salary,entry_date,resume) values(4,‘赵楠‘,‘男‘,‘1986-11-23‘,3800,‘2011-2-18‘,‘绝种好男人‘);

// 查看表的所有记录
select * from employee;

// 查看数据使用的所有编码
show variables like ‘character%‘;

// 修改客户端的编码 为 gbk
set character_set_client=gbk;

// 修改结果集的编码为gbk
set character_set_results=gbk;

// insert 语句的其他写法
create table a
(
    username varchar(20),
    password varchar(20)
);

insert into a values(‘zs‘,‘111‘);

insert into a values(‘wangwu‘,‘2222‘),(‘lisi‘,‘3333‘);

insert a values(‘aaa‘,‘bbb‘);

insert a (username) values(‘aaa‘);

2. update语句

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

将姓名为’zhangsan’的员工薪水修改为3000元。
updata employee set salary=2000 where name=‘zhangsan‘;

将姓名为’lisi’的员工薪水修改为4000元,sex改为female。
update employee set salary=4000,sex=‘female‘ where name=‘wangwu‘;

将xiaohong的薪水在原有基础上增加1000元
update employee set salary=salary+1000 where name=‘xiaohong‘;

3. delete语句

删除表中name为’赵楠’的记录。
delete from employee where name=‘赵楠‘;

删除表中所有记录。
delete from employee;

使用truncate删除表中记录。  摧毁表再创建表
truncate employee;

4. select语句
student.sql
create table student(
    id int,
    name varchar(20),
    chinese float,
    english float,
    math float
);

insert into student(id,name,chinese,english,math) values(1,‘a‘,89,78,90);
insert into student(id,name,chinese,english,math) values(2,‘b‘,67,53,95);
insert into student(id,name,chinese,english,math)values(2,‘c‘,67,53,95);
insert into student(id,name,chinese,english,math) values(3,‘e‘,87,78,77);
insert into student(id,name,chinese,english,math) values(4,‘f‘,88,98,92);
insert into student(id,name,chinese,english,math) values(5,‘d‘,82,84,67);
insert into student(id,name,chinese,english,math) values(6,‘g‘,55,85,45);
insert into student(id,name,chinese,english,math) values(7,‘h‘,75,65,30);

查询表中所有学生的信息。
select * 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;

过滤表中重复数据。
select distinct english from student;

在所有学生分数上加10分特长分。
select name,english+10,chinese+10,math+10 from student;

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

使用别名表示学生分数。

where 子句
查询姓名为李一的学生成绩
select * from student where name=‘李一‘;

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 name,english+chinese+math from student where english+chinese+math>200;

运算符
查询英语分数在 80－90之间的同学。
select * from student where english between 65 and 85;
查询数学分数为89,90,91的同学。
select name,math from student where math in(89,90,91);
查询所有姓李的学生成绩。
select * from student where name like ‘李%‘;
// 查询姓李的两个字的学生
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>80;
查询英语>80或者总分>200的同学
select *,chinese+math+english from student where english>80 or chinese+english+math>200;

order by 子句
对数学成绩排序后输出。
select * 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 *,chinese+math+english from student order by chinese+math+english desc;
对姓李的学生成绩排序输出
select * from student where name like ‘李%‘ order by chinese+math+english;

合计函数
count
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230的人数有多少？
select count(*) from student where chinese+math+english>230;

sum
统计一个班级数学总成绩？
select sum(math) from student;
select sum(math,chinese,english)from student;
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(math),sum(chinese),sum(english) from student; 
统计一个班级语文、英语、数学的成绩总和
select sum(math+chinese+english) from student;
统计一个班级语文成绩平均分
select sum(chinese)/count(*) from student;
缺考的不参与计算
select sum(chinese)/count(*) from student;
select sum(chinese)/count(chinese) from student;

avg
语文平均分
select avg(chinese) from student;
select avg(chinese) from student;
max/min
语文最高分
select max(chinese) from student;
select max(chinese) from student;
group by
create table orders(
    id int,
    product varchar(20),
    price float
);

insert into orders(id,product,price) values(1,‘电视‘,900);
insert into orders(id,product,price) values(2,‘洗衣机‘,100);
insert into orders(id,product,price) values(3,‘洗衣粉‘,90);
insert into orders(id,product,price) values(4,‘桔子‘,9);
insert into orders(id,product,price) values(5,‘洗衣粉‘,90);

将商品归类
select * from orders group by product;
select * from orders group by product;
select * from orders group by product;
select * from orders group by oId;
显示单类商品总结
select *,sum(price) from orders group by product;
i
商品分类 显示单类商品总价大于100的
select *,sum(price) from orders group by product having sum(price)>100;
select *,
// 将单价大于20 的商品进行归类显示  按照价格排序
select * from orders where price>20 group by product order by price;

四、表的约束
我们可以在创建表的同时为字段增加约束，对将来插入的数据做一些限定

唯一约束  unique
create table a
(
    name varchar(20) unique
);

insert into a values(‘aaa‘);
insert into a values(‘aaa‘); 错 name有唯一约束

非空约束 not null
create table b
(
    id int,
    name varchar(20) not null
);

insert into b values(1,‘aaa‘);

insert into b (id) values(2);    错，name有非空约束

主键  每张表都应该有个主键 方便我们找到记录 
主键必须有唯一约束、非空约束

主键约束 primary key
create table c
(
    id int primary key,
    name varchar(20) not null
);

insert into c (id,name) values(1,‘aaaa‘);

insert into c(id,name) values(1,‘bbbb‘); 错，主键重复
insert into c(name) values(‘ccc‘); 错，主键不能为null

主键可以定义为自动增长
create table d
(
    id int primary key auto_increment,
    name varchar(20)
);

insert into d(name) values(‘ccc‘);

insert into d(name) values(‘aaaa‘);

delete from d where id=4;

create table e
(
    id int,
    name varchar(20)
);