Redis键值设计

墨蓝 2023-10-17 15:34 6阅读 0赞

丰富的[数据结构][Link 1]使得[Redis][]的设计非常的有趣。不像关系型[数据库][Link 2]那样，DEV和DBA需要深度沟通，review每行sql语句，也不像memcached那样，不需要DBA的参与。[redis][Redis]的DBA需要熟悉数据结构，并能了解使用场景。

下面举一些常见适合kv数据库的例子来谈谈键值的设计，并与关系型数据库做一个对比，发现关系型的不足之处。

#### 用户登录系统 ####

记录用户登录信息的一个系统， 我们简化业务后只留下一张表。

##### 关系型数据库的设计 #####

mysql> select * from login;
    +---------+----------------+-------------+---------------------+
    | user_id | name           | login_times | last_login_time     |
    +---------+----------------+-------------+---------------------+
    |       1 | ken thompson   |           5 | 2011-01-01 00:00:00 |
    |       2 | dennis ritchie |           1 | 2011-02-01 00:00:00 |
    |       3 | Joe Armstrong  |           2 | 2011-03-01 00:00:00 |
    +---------+----------------+-------------+---------------------+

user\_id表的主键，name表示用户名，login\_times表示该用户的登录次数，每次用户登录后，login\_times会自增，而last\_login\_time更新为当前时间。

##### REDIS的设计 #####

关系型数据转化为KV数据库，我的方法如下：

key 表名：主键值：列名

value 列值

一般使用冒号做分割符，这是不成文的规矩。比如在[PHP][]\-admin for redis系统里，就是默认以冒号分割，于是user:1 user:2等key会分成一组。于是以上的关系数据转化成kv数据后记录如下：

Set login:1:login_times 5
    Set login:2:login_times 1
    Set login:3:login_times 2
    
    Set login:1:last_login_time 2011-1-1
    Set login:2:last_login_time 2011-2-1
    Set login:3:last_login_time 2011-3-1
    
    set login:1:name ”ken thompson“
    set login:2:name “dennis ritchie”
    set login:3:name ”Joe Armstrong“

这样在已知主键的情况下，通过get、set就可以获得或者修改用户的登录次数和最后登录时间和姓名。

一般用户是无法知道自己的id的，只知道自己的用户名，所以还必须有一个从name到id的映射关系，这里的设计与上面的有所不同。

set "login:ken thompson:id"      1
    set "login:dennis ritchie:id"    2
    set "login: Joe Armstrong:id"    3

这样每次用户登录的时候业务逻辑如下（[Python][]版），r是redis对象，name是已经获知的用户名。

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  </tr> 
 </tbody> 
</table>

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  </tr> 
 </tbody> 
</table>

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  </tr> 
 </tbody> 
</table>

如果需求仅仅是已知id，更新或者获取某个用户的最后登录时间，登录次数，关系型和kv数据库无啥区别。一个通过btree pk，一个通过hash，效果都很好。

假设有如下需求，查找最近登录的N个用户。开发人员看看，还是比较简单的，一个sql搞定。

<table style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; border-collapse:collapse!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important"> 
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   <td style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:3em!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(175,175,175)!important; font-size:10pt!important; vertical-align:top!important; top:auto!important; right:auto!important; left:auto!important"> <code style="margin:0px; position:static!important; text-align:right!important; padding:0px 0.3em 0px 0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:2.7em!important; bottom:auto!important; display:block!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">1</code></td> 
   <td style="border-left:3px solid rgb(108,226,108); margin:0px; position:static!important; padding:0px 0px 0px 0.5em!important; line-height:1.1em!important; border-right-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; border-top-width:0px!important; border-bottom-width:0px!important; height:auto!important; font-size:10pt!important; vertical-align:top!important; top:auto!important; right:auto!important; left:auto!important"> <code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,102,153)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; font-weight:bold!important; left:auto!important">select</code>&nbsp;<code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">*&nbsp;</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,102,153)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; font-weight:bold!important; left:auto!important">from</code>&nbsp;<code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">login&nbsp;</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,102,153)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; font-weight:bold!important; left:auto!important">order</code>&nbsp;<code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,102,153)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; font-weight:bold!important; left:auto!important">by</code>&nbsp;<code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">last_login_time&nbsp;</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,102,153)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; font-weight:bold!important; left:auto!important">desc</code>&nbsp;<code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">limit N</code></td> 
  </tr> 
 </tbody> 
</table>

DBA了解需求后，考虑到以后表如果比较大，所以在last\_login\_time上建个索引。执行计划从索引leafblock 的最右边开始访问N条记录，再回表N次，效果很好。

过了两天，又来一个需求，需要知道登录次数最多的人是谁。同样的关系型如何处理？DEV说简单

<table style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; border-collapse:collapse!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important"> 
 <tbody style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important"> 
  <tr style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important"> 
   <td style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:3em!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(175,175,175)!important; font-size:10pt!important; vertical-align:top!important; top:auto!important; right:auto!important; left:auto!important"> <code style="margin:0px; position:static!important; text-align:right!important; padding:0px 0.3em 0px 0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:2.7em!important; bottom:auto!important; display:block!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">1</code></td> 
   <td style="border-left:3px solid rgb(108,226,108); margin:0px; position:static!important; padding:0px 0px 0px 0.5em!important; line-height:1.1em!important; border-right-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; border-top-width:0px!important; border-bottom-width:0px!important; height:auto!important; font-size:10pt!important; vertical-align:top!important; top:auto!important; right:auto!important; left:auto!important"> <code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,102,153)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; font-weight:bold!important; left:auto!important">select</code>&nbsp;<code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">*&nbsp;</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,102,153)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; font-weight:bold!important; left:auto!important">from</code>&nbsp;<code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">login&nbsp;</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,102,153)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; font-weight:bold!important; left:auto!important">order</code>&nbsp;<code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,102,153)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; font-weight:bold!important; left:auto!important">by</code>&nbsp;<code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">login_times&nbsp;</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,102,153)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; font-weight:bold!important; left:auto!important">desc</code>&nbsp;<code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">limit N</code></td> 
  </tr> 
 </tbody> 
</table>

DBA一看，又要在login\_time上建立一个索引。有没有觉得有点问题呢，表上每个字段上都有素引。

关系型数据库的数据存储的的不灵活是问题的源头，数据仅有一种储存方法，那就是按行排列的堆表。统一的数据结构意味着你必须使用索引来改变sql的访问路径来快速访问某个列的，而访问路径的增加又意味着你必须使用统计信息来辅助，于是一大堆的问题就出现了。

没有索引，没有统计计划，没有执行计划，这就是kv数据库。

redis里如何满足以上的需求呢？ 对于求最新的N条数据的需求，链表的后进后出的特点非常适合。我们在上面的登录代码之后添加一段代码，维护一个登录的链表，控制他的长度，使得里面永远保存的是最近的N个登录用户。

<table style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; border-collapse:collapse!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important"> 
 <tbody style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important"> 
  <tr style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important"> 
   <td style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:3em!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(175,175,175)!important; font-size:10pt!important; vertical-align:top!important; top:auto!important; right:auto!important; left:auto!important"> <code style="margin:0px; position:static!important; text-align:right!important; padding:0px 0.3em 0px 0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:2.7em!important; bottom:auto!important; display:block!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">4</code></td> 
   <td style="border-left:3px solid rgb(108,226,108); margin:0px; position:static!important; padding:0px 0px 0px 0.5em!important; line-height:1.1em!important; border-right-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; border-top-width:0px!important; border-bottom-width:0px!important; height:auto!important; font-size:10pt!important; vertical-align:top!important; top:auto!important; right:auto!important; left:auto!important"> <code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">ret&nbsp;</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,102,153)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; font-weight:bold!important; left:auto!important">=</code>&nbsp;<code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">redis.ltrim(</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:blue!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">"login:last_login_times"</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">,&nbsp;</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,153,0)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">0</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">, N</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,102,153)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; font-weight:bold!important; left:auto!important">-</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,153,0)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">1</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">)</code></td> 
  </tr> 
 </tbody> 
</table>

这样需要获得最新登录人的id，如下的代码即可

<table style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; border-collapse:collapse!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important"> 
 <tbody style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important"> 
  <tr style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important"> 
   <td style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:3em!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(175,175,175)!important; font-size:10pt!important; vertical-align:top!important; top:auto!important; right:auto!important; left:auto!important"> <code style="margin:0px; position:static!important; text-align:right!important; padding:0px 0.3em 0px 0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:2.7em!important; bottom:auto!important; display:block!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">1</code></td> 
   <td style="border-left:3px solid rgb(108,226,108); margin:0px; position:static!important; padding:0px 0px 0px 0.5em!important; line-height:1.1em!important; border-right-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; border-top-width:0px!important; border-bottom-width:0px!important; height:auto!important; font-size:10pt!important; vertical-align:top!important; top:auto!important; right:auto!important; left:auto!important"> <code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">last_login_list&nbsp;</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,102,153)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; font-weight:bold!important; left:auto!important">=</code>&nbsp;<code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">r.lrange(</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:blue!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">"login:last_login_times"</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">,&nbsp;</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,153,0)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">0</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">, N</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,102,153)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; font-weight:bold!important; left:auto!important">-</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,153,0)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">1</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">)</code></td> 
  </tr> 
 </tbody> 
</table>

另外，求登录次数最多的人，对于排序，积分榜这类需求，sorted set非常的适合，我们把用户和登录次数统一存储在一个sorted set里。

zadd login:login_times 5 1
    zadd login:login_times 1 2
    zadd login:login_times 2 3

这样假如某个用户登录，额外维护一个sorted set，代码如此

<table style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; border-collapse:collapse!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important"> 
 <tbody style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important"> 
  <tr style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important"> 
   <td style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:3em!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(175,175,175)!important; font-size:10pt!important; vertical-align:top!important; top:auto!important; right:auto!important; left:auto!important"> <code style="margin:0px; position:static!important; text-align:right!important; padding:0px 0.3em 0px 0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:2.7em!important; bottom:auto!important; display:block!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">2</code></td> 
   <td style="border-left:3px solid rgb(108,226,108); margin:0px; position:static!important; padding:0px 0px 0px 0.5em!important; line-height:1.1em!important; border-right-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; border-top-width:0px!important; border-bottom-width:0px!important; height:auto!important; font-size:10pt!important; vertical-align:top!important; top:auto!important; right:auto!important; left:auto!important"> <code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">ret&nbsp;</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,102,153)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; font-weight:bold!important; left:auto!important">=</code>&nbsp;<code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">r.zincrby(</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:blue!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">"login:login_times"</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">,&nbsp;</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,153,0)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">1</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">, uid)</code></td> 
  </tr> 
 </tbody> 
</table>

那么如何获得登录次数最多的用户呢，逆序排列取的排名第N的用户即可

<table style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; border-collapse:collapse!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important"> 
 <tbody style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important"> 
  <tr style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important"> 
   <td style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:3em!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(175,175,175)!important; font-size:10pt!important; vertical-align:top!important; top:auto!important; right:auto!important; left:auto!important"> <code style="margin:0px; position:static!important; text-align:right!important; padding:0px 0.3em 0px 0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:2.7em!important; bottom:auto!important; display:block!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">1</code></td> 
   <td style="border-left:3px solid rgb(108,226,108); margin:0px; position:static!important; padding:0px 0px 0px 0.5em!important; line-height:1.1em!important; border-right-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; border-top-width:0px!important; border-bottom-width:0px!important; height:auto!important; font-size:10pt!important; vertical-align:top!important; top:auto!important; right:auto!important; left:auto!important"> <code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">ret&nbsp;</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,102,153)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; font-weight:bold!important; left:auto!important">=</code>&nbsp;<code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">r.zrevrange(</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:blue!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">"login:login_times"</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">,&nbsp;</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,153,0)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">0</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">, N</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,102,153)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; font-weight:bold!important; left:auto!important">-</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,153,0)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">1</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">)</code></td> 
  </tr> 
 </tbody> 
</table>

可以看出，DEV需要添加2行代码，而DBA不需要考虑索引什么的。

#### TAG系统 ####

tag在互联网应用里尤其多见，如果以传统的关系型数据库来设计有点不伦不类。我们以查找书的例子来看看redis在这方面的优势。

##### 关系型数据库的设计 #####

两张表，一张book的明细，一张tag表，表示每本的tag，一本书存在多个tag。

mysql> select * from book;
    +------+-------------------------------+----------------+
    | id   | name                          | author         |
    +------+-------------------------------+----------------+
    |    1 | The Ruby Programming Language | Mark Pilgrim   |
    |    1 | Ruby on rail                  | David Flanagan |
    |    1 | Programming Erlang            | Joe Armstrong  |
    +------+-------------------------------+----------------+
    
    mysql> select * from tag;
    +---------+---------+
    | tagname | book_id |
    +---------+---------+
    | ruby    |       1 |
    | ruby    |       2 |
    | web     |       2 |
    | erlang  |       3 |
    +---------+---------+
    
    假如有如此需求，查找即是ruby又是web方面的书籍，如果以关系型数据库会怎么处理？

<table style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; border-collapse:collapse!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important"> 
 <tbody style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important"> 
  <tr style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important"> 
   <td style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:3em!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(175,175,175)!important; font-size:10pt!important; vertical-align:top!important; top:auto!important; right:auto!important; left:auto!important"> <code style="margin:0px; position:static!important; text-align:right!important; padding:0px 0.3em 0px 0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:2.7em!important; bottom:auto!important; display:block!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">1</code></td> 
   <td style="border-left:3px solid rgb(108,226,108); margin:0px; position:static!important; padding:0px 0px 0px 0.5em!important; line-height:1.1em!important; border-right-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; border-top-width:0px!important; border-bottom-width:0px!important; height:auto!important; font-size:10pt!important; vertical-align:top!important; top:auto!important; right:auto!important; left:auto!important"> <code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,102,153)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; font-weight:bold!important; left:auto!important">select</code>&nbsp;<code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">b.</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,102,153)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; font-weight:bold!important; left:auto!important">name</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">, b.author&nbsp;&nbsp;</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,102,153)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; font-weight:bold!important; left:auto!important">from</code>&nbsp;<code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">tag t1, tag t2, book b</code></td> 
  </tr> 
 </tbody> 
</table>

<table style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; border-collapse:collapse!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important"> 
 <tbody style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important"> 
  <tr style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important"> 
   <td style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:3em!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(175,175,175)!important; font-size:10pt!important; vertical-align:top!important; top:auto!important; right:auto!important; left:auto!important"> <code style="margin:0px; position:static!important; text-align:right!important; padding:0px 0.3em 0px 0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:2.7em!important; bottom:auto!important; display:block!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">2</code></td> 
   <td style="border-left:3px solid rgb(108,226,108); margin:0px; position:static!important; padding:0px 0px 0px 0.5em!important; line-height:1.1em!important; border-right-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; border-top-width:0px!important; border-bottom-width:0px!important; height:auto!important; font-size:10pt!important; vertical-align:top!important; top:auto!important; right:auto!important; left:auto!important"> <code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(0,102,153)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; font-weight:bold!important; left:auto!important">where</code>&nbsp;<code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">t1.tagname =&nbsp;</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:blue!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">'web'</code>&nbsp;<code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(128,128,128)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">and</code>&nbsp;<code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">t2.tagname =&nbsp;</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:blue!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">'ruby'</code>&nbsp;<code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(128,128,128)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">and</code>&nbsp;<code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">t1.book_id = t2.book_id&nbsp;</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; color:rgb(128,128,128)!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">and</code><code style="margin:0px; position:static!important; padding:0px!important; line-height:1.1em!important; border-width:0px!important; outline-width:0px!important; width:auto!important; bottom:auto!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; float:none!important; height:auto!important; font-size:10pt!important; vertical-align:baseline!important; top:auto!important; right:auto!important; left:auto!important">b.id = t1.book_id</code></td> 
  </tr> 
 </tbody> 
</table>

tag表自关联2次再与book关联，这个sql还是比较复杂的，如果要求即ruby，但不是web方面的书籍呢？

关系型数据其实并不太适合这些集合操作。

##### REDIS的设计 #####

首先book的数据肯定要存储的，和上面一样。

set book:1:name    ”The Ruby Programming Language”
    Set book:2:name     ”Ruby on rail”
    Set book:3:name     ”Programming Erlang”
    
    set book:1:author    ”Mark Pilgrim”
    Set book:2:author     ”David Flanagan”
    Set book:3:author     ”Joe Armstrong”

tag表我们使用集合来存储数据，因为集合擅长求交集、并集

sadd tag:ruby 1
    sadd tag:ruby 2
    sadd tag:web 2
    sadd tag:erlang 3

那么，即属于ruby又属于web的书？

inter_list = redis.sinter("tag.web", "tag:ruby")

即属于ruby，但不属于web的书？

inter_list = redis.sdiff("tag.ruby", "tag:web")

属于ruby和属于web的书的合集？

inter_list = redis.sunion("tag.ruby", "tag:web")

简单到不行阿。

从以上2个例子可以看出在某些场景里，关系型数据库是不太适合的，你可能能够设计出满足需求的系统，但总是感觉的怪怪的，有种生搬硬套的感觉。

尤其登录系统这个例子，频繁的为业务建立索引。放在一个复杂的系统里，ddl（创建索引）有可能改变执行计划。导致其它的sql采用不同的执行计 划，业务复杂的老系统，这个问题是很难预估的，sql千奇百怪。要求DBA对这个系统里所有的sql都了解，这点太难了。这个问题在[Oracle][]里尤其严 重，每个DBA估计都碰到过。对于[MySQL][Link 2]这类系统，ddl又不方便（虽然现在有online ddl的方法）。碰到大表，DBA凌晨爬起来在业务低峰期操作，这事我没少干过。而这种需求放到redis里就很好处理，DBA仅仅对容量进行预估即可。

未来的OLTP系统应该是kv和关系型的紧密结合。

来源:http://blog.csdn.net/iloveyin/article/details/7105181

[Link 1]: http://lib.csdn.net/base/datastructure
[Redis]: http://lib.csdn.net/base/redis
[Link 2]: http://lib.csdn.net/base/mysql
[PHP]: http://lib.csdn.net/base/php
[Python]: http://lib.csdn.net/base/python
[Oracle]: http://lib.csdn.net/base/oracle