创建用户：?命令:CREATE USER “username” IDENTIFIED BY “password”;
授权用户：
命令:GRANT privileges ON databasename.tablename TO ”username“
设置更改密码：
命令:SET PASSWORD FOR ”username“ = PASSWORD(“newpassword”);
撤销用户权限：
命令: REVOKE privilege ON databasename.tablename FROM “username”;
privilege代表:select ,insert,update,所有用all代替
如果是所有数据库的所有表可以这样写"*.*"
删除用户
命令: DROP USER “username”;
