Mysql 展平对SQL查询的响应

我正在尝试用mysql为问答表创建一个平面表。这是我的桌子

波尔问题

PollID | Question| A | B | C | D | E | TimeStamp

花粉反应

PollReponseID | PollID | UserID | Answer

在

PollAnswer

表中，我得到了五个答案，分别是

VARCHAR

A、B、C、D、E

    select q.Question
     , q.PollID
     , r.Answer
     , count(r.Answer) 
  from pollQuestions q
     , pollResponse r
 where  q.PollID = r.PollID 
 group 
    by r.Answer
     , q.Question
     , q.PollID 
 order 
    by r.PollID;

我写了一个查询，按照

a、B、C、D、E

对答案进行分组

    select q.Question
     , q.PollID
     , r.Answer
     , count(r.Answer) 
  from pollQuestions q
     , pollResponse r
 where  q.PollID = r.PollID 
 group 
    by r.Answer
     , q.Question
     , q.PollID 
 order 
    by r.PollID;

我的回答如下

Question | PollID | Answer | count
alpha    |  1     | A     | 2 
alpha    |  1     | B     | 3 
alpha    |  1     | C     | 4 
alpha    |  1     | D     | 0
alpha    |  1     | E     | 0 
betas    |  2     | A     | 3 
betas    |  2     | B     | 4 
betas    |  2     | C     | 4 
betas    |  2     | D     | 6
betas    |  2     | E     | 0 

我想像这样把答案压平

Question | PollID | countA | countB | countC | countD | countE
alpha    |  1     | 2      | 2      |  4     |  0     |   0 
betas    |  2     | 3      | 4      |  4     |  6     |   0 

我是否可以在不改变表结构的情况下实现这一点

---

任何指示都将不胜感激

您可以尝试使用条件聚合函数

select 
    pollQuestions.Question, 
    pollQuestions.PollID, 
    count(CASE WHEN pollResponse.Answer ='A' THEN 1 END) countA,
    count(CASE WHEN pollResponse.Answer ='B' THEN 1 END) countB,
    count(CASE WHEN pollResponse.Answer ='C' THEN 1 END) countC,
    count(CASE WHEN pollResponse.Answer ='D' THEN 1 END) countD,
    count(CASE WHEN pollResponse.Answer ='E' THEN 1 END) countE
from pollQuestions 
JOIN pollResponse on pollQuestions.PollID = pollResponse.PollID  
group by 
    pollQuestions.Question,
    pollQuestions.PollID  
order by  
    pollResponse.PollID;

注意

---

我会使用

JOIN

而不是逗号

，

，因为

JOIN

语法比

更清晰，

关于连接两个表。

您可以使用

分组依据
和
求和（当…）时的情况，如下所示：

select pq.Question, pq.PollID,
       sum(case when pr.Answer = 'A' then 1 else 0 end) as 'countA',
       sum(case when pr.Answer = 'B' then 1 else 0 end) as 'countB',
       sum(case when pr.Answer = 'C' then 1 else 0 end) as 'countC',
       sum(case when pr.Answer = 'D' then 1 else 0 end) as 'countD',
       sum(case when pr.Answer = 'E' then 1 else 0 end) as 'countE'
from PollQuestion pq
left join PollResponse pr on pq.PollID = pr.PollID
group by pq.Question, pq.PollID

考虑应用程序代码中的数据显示问题