计算每个唯一值的出现次数 [英] Count number of occurrences for each unique value

问题描述

基本上我有一个类似这样的表：

  time ..... activities ..... length 
 13:00 ........ 3 ............. 1 
 13:15 ........ 2 ..... ........ 2 
 13:00 ........ 3 ............. 2 
 13:30 .... .... 1 ............. 1 
 13:45 ........ 2 ............. 3 
 13:15 ........ 5 ............. 1 
 13:45 ........ 1 ..... ........ 3 
 13:15 ........ 3 ............. 1 
 13:45 .... .... 3 ............. 2 
 13:45 ........ 1 ............. 1 
 13:15 ........ 3 ............. 3 
  

几个注释：

• 活动可介于1到5之间


• 长度可介于1到3之间。

查询应返回：

 时间........计数
 13:00 ......... 2 
 13:15 .... ..... 2 
 13:30 ......... 0 
 13:45 ......... 1 
  
 
 
 
基本上对于每个唯一的时间，我想要一个活动值为3的行数。
 
 
 
那么我可以这样说：
 在13:00有X个活动3s。 
在13:45有Y数量的活动3s。 
  
然后我想要计数活动1s，2s，4s和5s。所以我可以绘制每个独特时间的分布。
解决方案
是的，你可以使用 / code>：
 按时间，活动从表组中选择时间，活动， 
  
 
Basically I have a table similar to this:
time.....activities.....length  
13:00........3.............1  
13:15........2.............2  
13:00........3.............2  
13:30........1.............1  
13:45........2.............3  
13:15........5.............1  
13:45........1.............3  
13:15........3.............1  
13:45........3.............2  
13:45........1.............1  
13:15........3.............3  
A couple of notes:



Activities can be between 1 and 5
Length can be between 1 and 3


The query should return:
time........count  
13:00.........2  
13:15.........2  
13:30.........0  
13:45.........1  
Basically for each unique time I want a count of the number of rows where the activities value is 3.

So then I can say: 
At 13:00 there were X amount of activity 3s.
At 13:45 there were Y amount of activity 3s.
Then I want a count for activity 1s,2s,4s and 5s. so I can plot the distribution for each unique time.
解决方案
Yes, you can use group by:
select time, activities, count(*) from table group by time, activities;


                        
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