一、修改密码
mysql -u root -p
update setauthentication_string=password(“新密码”) where User="test" and Host="localhost";
flush privileges;
mysql5.7以后：表中没有了password字段，而是使用authentication_string来代替。
mysql5.7之前：update set password=password("123456") where user="root";（修改root的密码）;
二、删除用户
mysql -u root -p
Delete FROM Where User="用户名" and Host="localhost";
flush privileges;
创建用户
命令:CREATE USER 'username'@'host' IDENTIFIED BY 'password';
删除账户及权限：
drop user 用户名@’%’;
drop user 用户名@ localhost;
三、为用户授权
授权格式：grant 权限 on 数据库.* to 用户名@登录主机 identified by “密码”;
eg: grant all privileges on *.* to 'root'@'192.168.218.128' identified by 'hello' with grant option;//赋予用户所有数据库的权限以及创建数据库的权限
flush privileges; //要刷新权限
授权test用户拥有testDB数据库的所有权限：
grant all privileges on testDB.* to "test"@"localhost" identified by "1234";
flush privileges; #刷新系统权限表
指定部分权限给用户:
grant select,update on testDB.* to "test"@"localhost" identified by "1234";
flush privileges; #刷新系统权限表
四、显示当前用户信息
select user();