含义

通用唯一识别码 (Universally Unique Identifier)

作用

是让分布式系统中的所有元素，都能有唯一的辨识资讯，而不需要透过中央控制端来做辨识资讯的指定

表示方法

• 标准 4B-2B-2B-2B-6B(xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx)
• 微软(GUID) 4B-2B-2B-8B(xxxxxxxx-xxxx- xxxx-xxxxxxxxxxxxxxxx)

原理

MAC地址：故意情况下可重复；
机器标识：Java下就是JVM标识，故意情况下可重复；
纳秒级当前时间：故意情况下可重复；
随机数：小概率重复；
自增序列数（或时钟序列）：循环溢出时重复；

功能

• hex

  字符串转换为对应的ASCII码的16进制字符串

  数字转换为16进制字符串

• unhex

  将16进制数转换为字符串

1. 添加源仓库到pacman

   vi /etc/pacman.conf
   
   [archlinuxfr]
   SigLevel = Never
   Server = http://repo.archlinux.fr/$arch
   

2. 更新安装

   pacman -Sy yaourt
   

3. 安装拓展

   yaourt -S aurvote customizepkg rsync
   

1. vi /etc/pacman.conf

   # Misc options
   Color
   ILoveCandy
   

• 获取排序中指定序号列

  SELECT stockid, close/10000, pctchg/100, transday FROM stock_app.t_k_line_day WHERE stockid=? ORDER BY transday DESC LIMIT 1,1
  

• mysql下使用update set from select

  UPDATE friends INNER JOIN users ON friends.friendid=users.userid 
  SET friends.friendname=users.username
  

• 判断等于NULL

  is NULL
  

• 取指定数目数据

  select transday,preclose from t_k_line_day where '601866.SH' = stockid order by transday desc limit 10;
  

• 修改列名和定义

  alter table t_day_recommand change column proce price selectprice int(11);
  

• 修改列定义

  alter table t_day_recommand modify column inperiod int(11) DEFAULT NULL AFTER period;
  

• 添加列

  alter table t_product add column `issue_index` bigint NOT NULL COMMENT '发行点数, 用来计算份数' after issue_time;
  

• 命令行执行sql

  mysql -e "select * ...."
  

• 选择最大值，作为某个比较条件！

  select a.period, a.stockid, b.stockname, c.preclose, 
      (select count(userid) as count from t_follow_buy where stockid = a.stockid and status = 1) as followcount, 
      (a.highestprice - a.selectprice) / a.selectprice as maxincrease
      from stock_app.t_day_recommand a, stock_app.t_stock_base b, stock_app.t_realtime_quotation c 
      where a.priority = 0 and a.stockid = b.stockid and a.stockid = c.stockid and a.period = (select max(period) from t_day_recommand)
      ;
  

• update select

  UPDATE table1 alias
  SET (column_name,column_name ) = (
  SELECT (column_name, column_name)
  FROM table2
  WHERE column_name = alias.column_name)
  WHERE column_name = VALUE
  

• update table by select

  UPDATE table1 dest, (SELECT * FROM table2 where id=x) src 
  SET dest.col1 = src.col1 where dest.id=x ;
  

• Insert to table or update if exists

  INSERT INTO table (id, name, age) VALUES(1, "A", 19) ON DUPLICATE KEY UPDATE    
  name=VALUES(name), age=VALUES(age)
  

  1. http://stackoverflow.com/questions/4205181/insert-to-table-or-update-if-exists-mysql
  2. http://dev.mysql.com/doc/refman/5.1/en/insert-on-duplicate.html

• 查看mysql用户登录

  select host,user from mysql.user;
  

• 获取最近天的数据

  SELECT *
  FROM t_k_line_minute
  WHERE stockid="000300.SH" AND DATE(transminute) = (select max(date(transminute)) from t_k_line_minute where stockid = '000300.SH')
  ;
  

• 删除二进制日志

  PURGE BINARY LOGS TO 'mysql-bin.03';
  PURGE BINARY LOGS BEFORE 201506150000;
  

• 查看warnings

  show warnings;
  

• 删除原有主键，增加ID主键

  alter table TABLENAME drop primary key;
  alter table TABLENAME add column id bigint unsigned primary key auto_increment;
  

• 授权

  grant all privileges on nxb.* to 'dbgateway'@'%' identified by 'xianji';
  

• insert by select

  insert into banner_2_0_0 select * from t_banner_100;
  

• 修改数据库属性

  ALTER DATABASE db_aofei_test CHARACTER SET utf8 COLLATE utf8_unicode_ci;
  

• 设置auto_increment起始值

  ALTER TABLE tbl AUTO_INCREMENT = 100;
  

资源

• 阿里

• 58

  实现思路

好处

• 维持实体完整性

• 大大加快查询速度

• 查询结果，默认按着主键排序

• SELECT CAST(‘123’ AS SIGNED);

• SELECT CONVERT(‘123’,SIGNED);

• SELECT ‘123’+0;

环境

• ArchLinux

步骤

1. 安装模块

   pacman -S virtualbox-guest-modules
   

2. 手动载入模块

   modprobe -a vboxsf
   

   若提示Module not found，则执行：

   depmod $(uname -r)
   

3. 开机自动载入模块

   echo vboxsf >/etc/modules-load.d/virtualbox.conf
   

4. 创建挂载点

   mkdir /data
   

5. 在虚拟机控制中，加入共享文件夹

   E_DRIVE
   

6. 挂载

   • 手动挂载

     mount -t vboxsf E_DRIVE /data
     

   • 自动挂载

     /etc/fstab
     
     E_DRIVE /data vboxsf
     

常见问题

• 挂载失败

  错误提示：

  [cpp] view plaincopy
  mount: wrong fs type, bad option, bad superblock on E_DRIVE,
         missing codepage or helper program, or other error
         (for several filesystems (e.g. nfs, cifs) you might
         need a /sbin/mount.<type> helper program)
         In some cases useful info is found in syslog - try
         dmesg | tail or so
  

  解决过程：

  1. dmesg | tail

     sf_read_super_aux err=-22

  2. 查看vboxsf链接

     vincent@vincent-VirtualBox:/mnt$ ls -al /sbin/mount.vboxsf
     lrwxrwxrwx 1 root root 40 Jun 19 09:38 /sbin/mount.vboxsf -> /usr/lib/VBoxGuestAdditions/mount.vboxsf
     

  3. 发现链接不对，重新链接

     ln -s /opt/VBoxGuestAdditions-4.3.10/lib/VBoxGuestAdditions/mount.vboxsf /sbin/mount.vboxsf
     

参考

1. https://wiki.archlinux.org/index.php/VirtualBox#Installation_steps_for_Arch_Linux_guests

• 查看某个命令帮助

  ./manage.py help command
  

• 生成migrate操作

  python manage.py makemigrations
  

• 执行migrate操作

  ./manage.py migrate
  

• 生成多个数据库(1次migrate执行一个数据库)

  ./manage.py migrate
  ./manage.py migrate --database=stock_app
  

• 创建用户

  ./manage.py createsuperuser
  

• 修改用户密码

  ./manager.py changepasswd USERNAME