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SQL 行列倒置

SQL的的行列倒置已经不是新知识了,但在博主的技术咨询期间,仍发现其实有很多人并不了解这块,所以在此专门写一篇博客记录。本文将以Mysql为例,并以数据采集指标信息获取为例子。在下面的例子,你可以在sqlfiddle运行。

首先我们需要创建数据库Schema:

    CREATE TABLE Chart  (`createTime` DateTime, `kpi` varchar(30), `field` varchar(30), `value` double);     INSERT INTO Chart  (`createTime`,`kpi`, `field`, `value`)     VALUES  ("2015-02-01 12:00:00", 'disk', 'disk', 20),  ("2015-02-01 12:15:00", 'disk', 'disk', 30),  ("2015-02-01 12:20:00", 'disk', 'disk', 25),  ("2015-02-01 12:30:00", 'disk', 'disk', 25),  ("2015-02-01 12:35:00", 'disk', 'disk', 25),  ("2015-02-01 12:40:00", 'disk', 'disk', 25),  ("2015-02-01 12:00:00", 'disk', 'disk-all', 20),  ("2015-02-01 12:20:00", 'disk', 'disk-all', 30),  ("2015-02-01 12:25:00", 'disk', 'disk-all', 25),  ("2015-02-01 12:30:00", 'disk', 'disk-all', 25),  ("2015-02-01 12:35:00", 'disk', 'disk-all', 25),  ("2015-02-01 12:40:00", 'disk', 'disk-all', 25),  ("2015-02-01 12:40:00", 'cpu', 'cpu-all', 25),  ("2015-02-01 12:40:00", 'cpu', 'cpu', 25)     ;  

在这里字段分别代表:createTime = 数据采集时间,kpi = 数据采集指标,field = 作为指标的小类(一个kpi可以包含多个field),value = 采集的数据

当我们创建好了数据结构,下面因为我们希望获取出所有的 固定时间范围内的特定kpi的数据,注意因为可能一个kpi中的多个field,但是某些field漏采了部分时间的数据,所以这里我们需要补充异常点0. 并由于EChart这类图表库,希望我们输入的是横轴和纵轴为两个独立的数组对象表示。所以我们需要如下:

option = {  ....  xAxis : [   {    type : 'category',    boundaryGap : false,    data : ['周一','周二','周三','周四','周五','周六','周日']   }  ],  yAxis : [   {    type : 'value',    axisLabel : {     formatter: '{value} °C'    }   }  ],  series : [   {    ....    data:[11, 11, 15, 13, 12, 13, 10]   },   {      ....    data:[11, 11, 15, 13, 12, 13, 10]   }  ] };  

取出横轴比较容易,如下:

SELECT createTime,kpi, field, value FROM Chart WHERE kpi = 'disk' and (createTime BETWEEN '2015-02-01 12:00:00' AND '2015-02-01 12:25:00'); 

但是纵轴如果我们以同样方式取出,可能存在需要我们自动程序补值,并且需要保证每项数据和横轴对应,所以我们的程序处理会比较复杂,如下:

SELECT createTime,kpi, field, value FROM Chart WHERE kpi = 'disk' and (createTime BETWEEN '2015-02-01 12:00:00' AND '2015-02-01 12:25:00'); 

结果为:

createTime  kpi field   value February, 01 2015 12:00:00  disk    disk    20 February, 01 2015 12:15:00  disk    disk    30 February, 01 2015 12:20:00  disk    disk    25 February, 01 2015 12:00:00  disk    disk-all    20 February, 01 2015 12:20:00  disk    disk-all    30 February, 01 2015 12:25:00  disk    disk-all    25 

有没有其他方案更佳的呢?当然那就是本文要说的sql的倒置,如果我们能够把返回数据转换为如下:

field   ‘2015-02-01 12:00:00’   ‘2015-02-01 12:15:00’   ‘2015-02-01 12:20:00’   ‘2015-02-01 12:25:00’ disk         20                            30                     25                       0 disk-all     20                             0                     30                       25 

那么程序就很好处理了。在上面我们已经能够取出所有的横轴数据并排序,接下来我们将可以很简单的做到行列倒置:如下:

SELECT field, SUM(IF(createTime = '2015-02-01 12:00:00', value, 0)) as '2015-02-01 12:00:00', SUM(IF(createTime = '2015-02-01 12:15:00', value, 0)) as '2015-02-01 12:15:00', SUM(IF(createTime = '2015-02-01 12:20:00', value, 0)) as '2015-02-01 12:20:00', SUM(IF(createTime = '2015-02-01 12:25:00', value, 0)) as '2015-02-01 12:25:00'  FROM Chart WHERE kpi = 'disk' and (createTime BETWEEN '2015-02-01 12:00:00' AND '2015-02-01 12:25:00') GROUP BY field 

这样返回数据满足我们的需求了。

下面我们来分析下这句SQL,

  1. 首先我们利用‘IF(createTime = ‘2015-02-01 12:00:00’, value, 0)’来处理插值,并对每行数据转为以时间为列数据,并可以利用IF来补’0‘,将会如下:

SQL:

SELECT field, IF(createTime = '2015-02-01 12:00:00', value, 0) as '2015-02-01 12:00:00', IF(createTime = '2015-02-01 12:15:00', value, 0) as '2015-02-01 12:15:00', IF(createTime = '2015-02-01 12:20:00', value, 0) as '2015-02-01 12:20:00', IF(createTime = '2015-02-01 12:25:00', value, 0) as '2015-02-01 12:25:00'  FROM Chart WHERE kpi = 'disk' and (createTime BETWEEN '2015-02-01 12:00:00' AND '2015-02-01 12:25:00'); 

结果为:

field   ‘2015-02-01 12:00:00’   ‘2015-02-01 12:15:00’   ‘2015-02-01 12:20:00’   ‘2015-02-01 12:25:00’ disk               20                       0                       0                       0 disk                0                       30                      0                       0 disk                0                       0                       25                      0 disk-all            20                      0                       0                       0 disk-all            0                       0                       30                      0 disk-all            0                       0                       0                       25 
  1. 这下我们就可以利用sql的聚合函数sum和group by来聚合数据行:

SQL:

SELECT field, SUM(IF(createTime = '2015-02-01 12:00:00', value, 0)) as '2015-02-01 12:00:00', SUM(IF(createTime = '2015-02-01 12:15:00', value, 0)) as '2015-02-01 12:15:00', SUM(IF(createTime = '2015-02-01 12:20:00', value, 0)) as '2015-02-01 12:20:00', SUM(IF(createTime = '2015-02-01 12:25:00', value, 0)) as '2015-02-01 12:25:00'  FROM Chart WHERE kpi = 'disk' and (createTime BETWEEN '2015-02-01 12:00:00' AND '2015-02-01 12:25:00') GROUP BY field 

效果如上。

对于sql行列转置可以简述为分为两部分:

  1. 利用条件逻辑(mysql: IF, sql server: case … when ..)将 需要倒置的数据变为列。
  2. 利用聚合函数(sum、max、min…)group by 合并数据。这里需要注意max、min需要注意数据的边界,如存在负数且默认值采用0,那么max就会存在问题,所以一般sum是最安全的(任何数加0都不会改变结果);但对于特定场景max、min也是安全方案。
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