日志表设计一例分析

关于关系表的设计归根结底有两个方面。
第一，就是完全按照范式理论去设计，一般来说达到第三范式就可以了，或者你可以划分的更细到达更上一层次。比如第四，第五，第六等等。这种设计有自己的可读性很强，但是有一点，在检索数据的时候增加了多张关系表来做关联的开销。
第二，就是在范式理论上适当的做些反范式，有的东西还是不要太剥离的好。（窄表以及宽表） 这点和软件设计中的紧耦合松耦合理论一致。


下面我就以常用的LOG表来做下演示，其中有两种表的实际，一种是窄表，一种是稍微宽一点的表。
窄表：log_ytt

mysql> show create table log_ytt;    
+-------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table       | Create Table                                                                                                                                                             |
+-------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| log_ytt | CREATE TABLE `log_ytt` (
  `ids` bigint(20) DEFAULT NULL,
  `log_time` datetime DEFAULT NULL,
  KEY `idx_u1` (`ids`,`log_time`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 | 
+-------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

表记录数

mysql>  select * from log_ytt where ids > '4875000001';                                                                                    +------------+---------------------+
| ids        | log_time            |
+------------+---------------------+
| 7110000001 | 2014-05-20 21:56:42 | 
| 6300000001 | 2014-05-20 21:56:42 | 
| 6750000001 | 2014-05-20 21:56:42 | 
| 5310000001 | 2014-05-20 21:56:42 | 
| 7200000001 | 2014-05-20 21:56:42 | 
| 7380000001 | 2014-05-20 21:56:42 | 
| 5760000001 | 2014-05-20 21:56:42 | 
| 6930000001 | 2014-05-20 21:56:42 | 
| 6660000001 | 2014-05-20 21:56:42 | 
| 5670000001 | 2014-05-20 21:56:42 | 
| 6210000001 | 2014-05-20 21:56:42 | 
| 5850000001 | 2014-05-20 21:56:42 | 
| 6570000001 | 2014-05-20 21:56:42 | 
| 5580000001 | 2014-05-20 21:56:42 | 
| 5130000001 | 2014-05-20 21:56:42 | 
| 7290000001 | 2014-05-20 21:56:42 | 
| 6390000001 | 2014-05-20 21:56:42 | 
| 5490000001 | 2014-05-20 21:56:42 | 
| 5220000001 | 2014-05-20 21:56:42 | 
| 7560000001 | 2014-05-20 21:56:42 | 
| 7470000001 | 2014-05-20 21:56:42 | 
| 7020000001 | 2014-05-20 21:56:42 | 
| 6840000001 | 2014-05-20 21:56:42 | 
| 6030000001 | 2014-05-20 21:56:42 | 
| 6480000001 | 2014-05-20 21:56:42 | 
| 7650000001 | 2014-05-20 21:56:42 | 
| 5940000001 | 2014-05-20 21:56:42 | 
| 6120000001 | 2014-05-20 21:56:42 | 
| 7740000001 | 2014-05-20 21:56:42 | 
| 5400000001 | 2014-05-20 21:56:42 | 
| 5760000001 | 2014-05-21 03:19:07 | 
| 6840000001 | 2014-05-21 03:19:17 | 
| 7020000001 | 2014-05-21 03:19:32 | 
| 7200000001 | 2014-05-21 03:19:45 | 
| 7110000001 | 2014-05-21 03:19:46 | 
| 7380000001 | 2014-05-21 03:19:48 | 
| 5670000001 | 2014-05-21 03:19:58 | 
| 6930000001 | 2014-05-21 03:19:59 | 
| 6030000001 | 2014-05-21 03:20:00 | 
| 5940000001 | 2014-05-21 03:20:00 | 
| 7290000001 | 2014-05-21 03:20:02 | 
| 6120000001 | 2014-05-21 03:20:09 | 
| 5850000001 | 2014-05-21 03:20:18 | 
| 5580000001 | 2014-05-21 03:20:24 | 
| 6480000001 | 2014-05-21 03:25:05 | 
| 6390000001 | 2014-05-21 03:25:37 | 
| 6210000001 | 2014-05-21 03:25:45 | 
| 7470000001 | 2014-05-21 03:26:14 | 
| 6750000001 | 2014-05-21 03:27:17 | 
| 5310000001 | 2014-05-21 03:27:33 | 
| 5130000001 | 2014-05-21 03:27:34 | 
| 6570000001 | 2014-05-21 03:27:34 | 
| 7560000001 | 2014-05-21 03:27:45 | 
| 5220000001 | 2014-05-21 03:27:45 | 
| 5400000001 | 2014-05-21 03:27:53 | 
| 5490000001 | 2014-05-21 03:27:55 | 
| 6660000001 | 2014-05-21 03:28:07 | 
| 6300000001 | 2014-05-21 03:28:13 | 
| 7740000001 | 2014-05-21 03:28:26 | 
| 7650000001 | 2014-05-21 03:28:37 | 
+------------+---------------------+
60 rows in set (0.00 sec)

接下来，我们要检索所有IDS的平均时间。 有以下两种方式：
第一， 对表进行了两次访问，并且有GROUP BY 操作，不可取。

mysql> select sec_to_time(avg(timestampdiff(second,a.times,b.times)))  as 'running' 
    -> from 
    -> (select ids,min(log_time) as times from log_ytt where 1 group by ids ) as a,
    -> (select ids,max(log_time) as times from log_ytt where 1 group by ids) as b where a.ids = b.ids;
+---------------+
| running       |
+---------------+
| 05:27:08.8333 | 
+---------------+
1 row in set (0.00 sec)

第二，虽然对表进行了最少的访问，但是也有一次GROUP BY 操作。也没办法，表设计如此。

mysql> SELECT SEC_TO_TIME(AVG(times)) AS 'Running' FROM 
    -> (
    -> SELECT TIMESTAMPDIFF(SECOND,MIN(log_time),MAX(log_time)) AS times FROM log_ytt GROUP BY ids
    -> ) AS T;
+---------------+
| Running       |
+---------------+
| 05:27:08.8333 | 
+---------------+
1 row in set (0.00 sec)

宽表：log_ytt_horizontal.

mysql> show create table log_ytt_horizontal;
+------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table                  | Create Table                                                                                                                                                                                              |
+------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| log_ytt_horizontal | CREATE TABLE `log_ytt_horizontal` (
  `ids` bigint(20) NOT NULL,
  `start_time` datetime DEFAULT NULL,
  `end_time` datetime DEFAULT NULL,
  PRIMARY KEY (`ids`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 | 
+------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

表记录数：

mysql> select * from log_ytt_horizontal;
+------------+---------------------+---------------------+
| ids        | start_time          | end_time            |
+------------+---------------------+---------------------+
| 5130000001 | 2014-05-20 21:56:42 | 2014-05-21 03:27:34 | 
| 5220000001 | 2014-05-20 21:56:42 | 2014-05-21 03:27:45 | 
| 5310000001 | 2014-05-20 21:56:42 | 2014-05-21 03:27:33 | 
| 5400000001 | 2014-05-20 21:56:42 | 2014-05-21 03:27:53 | 
| 5490000001 | 2014-05-20 21:56:42 | 2014-05-21 03:27:55 | 
| 5580000001 | 2014-05-20 21:56:42 | 2014-05-21 03:20:24 | 
| 5670000001 | 2014-05-20 21:56:42 | 2014-05-21 03:19:58 | 
| 5760000001 | 2014-05-20 21:56:42 | 2014-05-21 03:19:07 | 
| 5850000001 | 2014-05-20 21:56:42 | 2014-05-21 03:20:18 | 
| 5940000001 | 2014-05-20 21:56:42 | 2014-05-21 03:20:00 | 
| 6030000001 | 2014-05-20 21:56:42 | 2014-05-21 03:20:00 | 
| 6120000001 | 2014-05-20 21:56:42 | 2014-05-21 03:20:09 | 
| 6210000001 | 2014-05-20 21:56:42 | 2014-05-21 03:25:45 | 
| 6300000001 | 2014-05-20 21:56:42 | 2014-05-21 03:28:13 | 
| 6390000001 | 2014-05-20 21:56:42 | 2014-05-21 03:25:37 | 
| 6480000001 | 2014-05-20 21:56:42 | 2014-05-21 03:25:05 | 
| 6570000001 | 2014-05-20 21:56:42 | 2014-05-21 03:27:34 | 
| 6660000001 | 2014-05-20 21:56:42 | 2014-05-21 03:28:07 | 
| 6750000001 | 2014-05-20 21:56:42 | 2014-05-21 03:27:17 | 
| 6840000001 | 2014-05-20 21:56:42 | 2014-05-21 03:19:17 | 
| 6930000001 | 2014-05-20 21:56:42 | 2014-05-21 03:19:59 | 
| 7020000001 | 2014-05-20 21:56:42 | 2014-05-21 03:19:32 | 
| 7110000001 | 2014-05-20 21:56:42 | 2014-05-21 03:19:46 | 
| 7200000001 | 2014-05-20 21:56:42 | 2014-05-21 03:19:45 | 
| 7290000001 | 2014-05-20 21:56:42 | 2014-05-21 03:20:02 | 
| 7380000001 | 2014-05-20 21:56:42 | 2014-05-21 03:19:48 | 
| 7470000001 | 2014-05-20 21:56:42 | 2014-05-21 03:26:14 | 
| 7560000001 | 2014-05-20 21:56:42 | 2014-05-21 03:27:45 | 
| 7650000001 | 2014-05-20 21:56:42 | 2014-05-21 03:28:37 | 
| 7740000001 | 2014-05-20 21:56:42 | 2014-05-21 03:28:26 | 
+------------+---------------------+---------------------+
30 rows in set (0.00 sec)

如果对这种稍微冗余一些的表来进行查询，那么对表的访问以及CPU的资源占用都达到了最低。

mysql> select sec_to_time(avg(timestampdiff(second,start_time,end_time))) as 'Running'  from log_ytt_horizontal;
+---------------+
| Running       |
+---------------+
| 05:27:08.8333 | 
+---------------+
1 row in set (0.00 sec)