包括在GROUP_CONCAT空结果

Question

我有两个表这样

profile_answers

+---------+------------+ 
|  id | class_name | 
+---------+------------+ 
|  1 | Class 1 | 
|  2 | Class 2 | 
|  3 | Class 1 | 
+---------+------------+ 

的教育

+---------+--------------------+------------+ 
|  id | profile_answers_id | sample | 
+---------+--------------------+------------+ 
|  1 | 1     |  1234 | 
|  2 | 1     |  2334 | 
|  3 | 1     |  3434 | 
+---------+------------+--------------------+ 

我跑的查询，

select educations.profile_answer_id, GROUP_CONCAT(educations.sample) from educations 
LEFT JOIN profile_answers ON educations.profile_answers_id = profile_answers.id 

我

+--------+--------------------+-------------+ 
|  id | sample       | 
+---------+--------------------+------------+ 
|  1 | 1234,2334,3434     | 
+---------+------------+--------------------+ 

其实我是想，

+--------+--------------------+-------------+ 
|  id | sample       | 
+---------+--------------------+------------+ 
|  1 | 1234,2334,3434     | 
|  2 | NULL       | 
|  3 | NULL       | 
+---------+------------+--------------------+ 

Answer 1

看起来像你缺少你GROUP BY：

select profile_answers.id, GROUP_CONCAT(educations.sample) 
from profile_answers 
LEFT JOIN educations ON educations.profile_answers_id = profile_answers.id 
GROUP BY profile_answers.id 

我也改变了自己的加入，使profile_answers表你的主桌。

祝你好运。

Answer 2

SELECT id,IFNULL(samples,'NULL') sample FROM 
(
    SELECT 
     AA.id, 
     GROUP_CONCAT(DISTINCT BB.sample) samples 
    FROM 
     profile_answers AA LEFT JOIN educations BB 
     ON AA.id = BB.profile_answers_id 
    GROUP BY AA.id 
) A;