mysql - SQL 查询 - 分组依据不起作用

Question

我有一个这样的表“Answer”:

Id, Registration_id, attendee_id, question_id, answer
12   Reg02                1             1        Paul
13   Reg02                1             2        Smith
14   Reg03                2             1        Rachel
15   Reg03                2             2        Silva

我的查询是:

Select attendee_id, answer
From wp_events_answer;                            

结果我得到了这个:

attendee_id  answer
    1         Paul
    1         Smith
    2         Rachel      
    2         Silva

但我想要这个:

 attendee_id  FirstName   Name
    1         Paul        Smith
    2         Rachel      Silva  

我添加了Group By attendee_id。但它仍然不起作用。结果它只显示这个:

 attendee_id    FirstName
 1              Paul
 2              Rachel

你能告诉我哪里出了问题吗？

谢谢

Answer 1

你不需要组，你需要一个自加入。

SELECT f.attendee_id, f.answer as FirstName, l.answer as Name
FROM wp_events_answer f
    JOIN wp_events_answer l ON f.attendee_id = l.attendee_id
WHERE f.question_id = 1 AND l.question_id = 2