1064表示语法错误
create database dsay00; 创建数据库
create database day00 character set urf8 ; 创建数据库指定字符集urf8
create database day00 character set utf8 collate utf8_bin;创建数据库指定字符集和校验规则
show databases；显示所有的数据库
show database day00;显示数据库的信息
show character set;显示MySQL支持的字符集gbk urf8;
show create database day00 ;显示创建数据库的字符集
show collation like 'utf8%';显示指定字符集下的校验规则
use day00 ;进入/切换对应的数据库
drop database day00;删除数据库
alter database day00 character set 'gbk';修改数据库的字符集
alter database day00 collate gbk_bin;修改校验规则
select database();获取当前正在使用的数据库
show tables ; 显示所有的表
show create table stu;查看创建的表
desc stu;显示一个表的详细信息
创建表
create table 数据表名(
列名 列类型[约束]，
列名 列类型，
列名 列类型
);
create table stu(
name varchar(大小),
age int,
num int,
birthday date
);
MySQL的数据类型
数值类型
tinyint
smallint
MEDIUMINT
int （最常用）
bigint
时间和日期类型
列类型
“零”值
DATETIME
'0000-00-00 00:00:00'
DATE
'0000-00-00'
TIMESTAMP (时间戳)
00000000000000
TIME
'00:00:00'
时间和时间戳的区别：
date:只包含日期，如果传入数据时，没有指定值，将是null
timestamp:包含日期和时间，如果传入的数据时，没有指定值，将是当前的系统时间
字符串类型
char和varchar型
CHAR列的长度固定为创建表时声明的长度。长度可以为从0到255的任何值
VARCHAR列中的值为可变长字符串。长度可以指定为0到65,535之间的值
char(character)定长，例如指定长度100，实际传入值为20，其余字符用空格补全
varchar(variable character)可变长度，例如：指定长度100，实际传入值20.实际存储就是20个字符
create table stu2(
name char(20),
age int,
birthday date,
login timestamp,
time time
);
insert into stu2 values('tom',10,'1998-10-10',null,'12:30:50');//插入数据
select * from stu;//查询数据
约束
not null 非空约束
unique 唯一 （但是null值不等于null值）
unique not null 唯一非空
primary key 主键约束 （非空唯一） auto_increment 自动增长
create table employee(
id int primary key auto_increment,
name varchar(10) not null,
phone_num varchar(15) unique
);
对表操作
删表
drop table temp;
修改表
添加列
alter table employee2
add hobby varchar(20);
删除列
alter table employee2
drop hobby;
修改列的长度
alter table employee2
modify name varchar(20);
修改列的数据类型
alter table employee2
modify name int;
修改列的名字
alter table employee2
change name score int;
重命名表名
1. rename table employee2 to emp;
2. alter table employee2
rename to tmp;
增删改查
insert
delect
update
select
插入数据
insert into 表名（列名1，列名2...） values（值1，值2...）;
insert into employee2(id,name) values(1,'kk');
insert into employee2(id,name,phone_num) values(02,'kk','1516666666');
//一般id列不用传值
insert into employee2 values(null,'xx','13945551544',1000);
insert into employee2 values(null,'张三','132884884',5000);
insert into employee2 values(null,'张三四','185445284',200);
insert into employee2 values(null,'李张王飞','1355444524',100);
insert into employee2 values(null,'章长张','11528452874',220);
insert into employee2 values(null,'李丽','195554525278',1200);
删除数据
delect from employee2 where id =2;
delect from employee2;清空表，保留表结构（逐条删）
truncate employee2;清空表，保留表结构（一次性把表删除，相当于drop table,接着创建一样的新空表）
修改数据
update employee2 set name = 'ss' where id = 2;
update employee2 set salary= salary+100 where id = 3;
查询数据
select 列名 from 表名 where 条件;
select * from employee2;
select name from employee2 where id>2;
select name,phone_num from employee2 where id>2;
//查询去重distinct
select distinct salary from employee2;
//查询之后的列进行运算
select salary+100 from employee2;
//查询之后取别名 as (as可以省略)
select salary+100 as new_salary from employee2;
中文乱码问题
客户端 服务器
cmd --> client -->server
1.临时设置cmd编码
mysql --dafault-character-set=gbk -uroot -proot
窗口关闭后失效
2.永久设置
修改配置文件 my.ini 57行 utf8改成GBK
重启mysql net stop mysql
net start mysql
常用符号
> < = <> !=
in(10,20,30)
like '张%' // %一个或多个字符
like '%张'
like '%张%' //只要包括张的
like '张_' // 只能匹配一个通配符
is null //判断空
is not null //判断非空
not
and
or
select* from stu where name = '李四';
select * from employee2 where salary in(1000,200,1200);
select * from employee2 where name like '张%';
select * from employee2 where name like '__';//两个下划线表示为两个字
select * from employee2 where name is null;
select * from employee2 where salary between 81 and 90;
select * from employee2 where salary 1000 or 2000;
排序
order by
asc 升序(默认)
desc 降序
select name,math,english from stu order by math asc,english desc;
select name,math+english as sum from stu order by sum desc;别名+排序
将所有姓张的同学的english成绩降序排列
select * from stu where name like '张%' order by english desc;
//创建学生表
create table stu(
id int primary key auto_increment,
name varchar(10) not null,
age varchar(15) unique ,
math int,
english int
);
insert into stu values(null,'李华','15',60,30);
insert into stu values(null,'李明','14',80,60);
insert into stu values(null,'张时','22',40,96);
insert into stu values(null,'王五','54',66,50);
insert into stu values(null,'天使','25',25,70);
insert into stu values(null,'魔鬼','12',90,52);
insert into stu values(null,'李四','31',98,90);
聚合函数，通常和分组一起使用
count() 计数
count(*)
select count(name) from stu;
select count(*) as count from stu;//查询记录取别名
select count(*) as count from stu where math>80;
select count(*) as count as sum from stu where sum>120;
求和
sum()
select sum(math) as sum from stu;
select sum(math) ,sum(english) from stu;
如果使用聚合函数 sum（） null 被当作0；
select sum(math)+sum(english) from stu;
当记录某列中有null值时，如果用+相加都为null;
select sum(math+english) from stu;
解决方法：使用ifnull(列名，指定默认值)函数解决相加为0问题
select sum(ifnull(math,0)+ifnull(english,0)) from stu;
平均值
avg()
select avg(math) from stu;
求max() min()
select max(math) from stu;
select min(english) from stu;
//创建销售记录表
create table orders(
id int primary key auto_increment,
product varchar(12) not null,
date timestamp,
price int
);
insert into orders values(null,'洗衣机',null,1000);
insert into orders values(null,'电视',null,2200);
insert into orders values(null,'电视',null,2200);
insert into orders values(null,'洗衣机',null,1000);
insert into orders values(null,'空调',null,5000);
insert into orders values(null,'洗衣机',null,1000);
insert into orders values(null,'空调',null,5000);
insert into orders values(null,'电视',null,2200);
分组操作 group by
group by having 后面加条件//对group by 后的结果再次进行过滤，不能用where用having
select * from 表名 where 条件 group by 列名 having分组后的条件 order by 列名desc/asc；
select product, sum(price) from orders group by product;
select product, sum(price) from orders where price>1000 group by product having sum(price) >10000;
//出错，应该加别名 select product, sum(price) from orders where price>1000 group by product having sum >10000;
select product, sum(price) as sum from orders where price>1000 group by product having sum >10000;
select product, sum(price) as sum from orders where price>1000 group by product having sum >10000 order by sum desc;