mysql官方测试库,点我
修改密码
mysqladmin -u root -p password 123
这条命令可以为用户设置密码,root位置为用户名,123 位置为密码,password不用改
查看连接线程
show processlist;
用户
create user hw@'%' identified by '123456'
hw 为用户名
% 可以访问的ip地址(% 代表所以ip地址)
123456 为密码
select user, host from mysql.user; 可以查询用户创建成功没
alter user hw@'%' identified by '123456' 可以修改密码
drop user hw@'%'; 删除用户
权限
grant all on *.* to root@'%' identified by 'password'
all 代表所有权限,可以换成
select等第一个* 是数据库名称，可以改成允许访问的数据库名称
第二个* 是数据库的表名称(*代表允许访问任意的表和数据库)
root代表远程登录使用的用户名，可以自定义
% 代表允许任意ip登录，如果你想指定特定的IP，替换掉就可以
password 是运程连接密码
with grant option命令可以加在后面,这只有root用户可以使用
show grants for root; 查看用户权限
revoke delete on *.* from root@'%' 回收delete权限
管理员忘记root用户密码
mysqld_safe --skip-grant-tables --skip-networking &
关闭连接层和tcp/ip连接
flush privileges;
alter user root@'%' identified by "123456";
DATABASE
create database hw CHARSET utf8mb4 collate utf8mb4_bin;
alter database hw charset utf8;
表
desc 表名 查看表的结构
create table test like stu; 创建一个和stu一样的表
表的修改
添加 alter table stu ADD qq varchar(20) NOT NULL UNIQUE comment "qq号";
指定位置添加 :
alter table stu ADD wechat varchar(20) NOT NULL UNIQUE AFTER sname COMMENT "微信";
alter table stu ADD num INT NOT null FIRST;
删除列 alter table stu DROP qq;
修改列的属性 alter table stu MODIFY sname varchar(12) NOT NULL;
修改列sgender为sg以及属性 alter table stu change sgender sg char(1) NOT NULL;
启动读文件
mysqld --help --verbose | grep my.cnf
可以查看读取的文件
查看支持字符集
show charset;
查看校对规则
show collation;
insert
INSERT INTO stu(sname,sage,sgender,sfz,intime) VALUES('hw',20,'f','123456',NOW());
同时录入多行数据
INSERT INTO stu(sname,sage,sgender,sfz)
VALUES
('hwe',20,'f','123456fe'),
('fe',43,'m','23');
update
UPDATE stu SET sname='zhao4' WHERE id=2; 修改id=2的sname为zhao4
delete
DELETE FROM stu WHERE id=3; delete 命令只是对信息标注不可见,不释放空间
TRUNCATE TABLE stu;
select
顺序:
select
from
where
group by
having
order by
limit
select @@xxx 查看系统参数
select @@port; 查看端口
select @@basedir; 查看目录
select @@datadir;
select @@socket;
select @@server_id;
select @@log_error;
select @@log_bin_basename;
show variables like 'innodb%';
select()函数
select NOW();
select DATABASE();
user() 当前用户
concat() 拼接字符串
group_concat() 一行显示
单表子句-where
where 等值查询
select * from city where country='china';
where 比较操作符
select * from city where population<100;
where 逻辑运算符(and, or)
select * from city where countrycode='CHN' AND population>500000;
where 模糊查询
select * from city where district LIKE 'guang%';
where in子句
select * from city where countrycode IN ('CHN', 'USA'); 和or功能相似
where between and
select * from city where population> 1000000 and population<2000000; =
select * from city where population BETWEEN 1000000 and 2000000;
单表子句-group by
聚合函数: max(),min()
avg() 平均数
sum() 总和
count() 个数
group_concat() 列转行
select countrycode,SUM(population) from city group by countrycode;
单表子句-having
select district,SUM(population)
from city
where countrycode='chn'
group by district
having sum(population)<1000000;
单表子句-order by
select * from city
where countrycode='chn'
order by population DESC;
DESC 降序(从大到小)
ASC 从小到大
select district,sum(population) from city
where coutrycode='chn'
group by district
having sum(population)>500000
order by sum(population) DESC;
单表子句-limit
前3名
select district,sum(population) from city
where coutrycode='chn'
group by district
having sum(population)>500000
order by sum(population) DESC
limit 3;
n 代表开始位置
m 代表显示数量
limit n,m
limit m offset n
单表子句-distinct
select distinct(countrycode) from city;
联合查询- union all
select * from city where countrycode='chn'
union all
select * from city where countrycode='usa';
一般情况下,会将 IN和 OR 语句改写成UNION ALL,来提高性能
union 去重复
union all 不去重复
多表连接
select employees.emp_no,salaries.salary from
employees join salaries
on employees.emp_no=salaries.emp_no
order by salaries.salary desc
limit 100;
