如何按两个不同的列对 MySQL 查询进行分组？

Question

我正在研究的问题是：

Provide the average answer for questions in broken down by Province and then by Question. You must include the province and the question as well as the average.

示例输出看起来像这样：

 Ontario - Do you like blak? - 3.4
 Ontario - Do you like flah? - 2.3
 Ontario - Do you like rahhggg? - 4.8
 Alberta - Do you like flah? - 2.3
 Alberta - Do you like rahhggg? - 4.8

到目前为止，我已经尝试按问题列出它们的平均值，但我不知道如何先按省分组。我认为这是一个 JOIN 但我不确定如何布置它。我有：

SELECT survey_question_id, AVG(survey_response)
FROM survey_responses
JOIN survey_responders 
ON survey_responses.id = survey_responders.id
WHERE survey_responders.province='Ontario'
GROUP BY survey_question_id;

Answer 1

SELECT province,survey_question_id, AVG(survey_response)
FROM survey_responses
JOIN survey_responders 
ON survey_responses.id = survey_responders.id
WHERE survey_responders.province='Ontario'
GROUP BY province,survey_question_id;

如果您需要所有省份，只需像这样删除 Where

SELECT province,survey_question_id, AVG(survey_response)
FROM survey_responses
JOIN survey_responders 
ON survey_responses.id = survey_responders.id
GROUP BY province,survey_question_id;

Answer 2

MySQL 中的 GROUP BY 语句决定了查询引擎如何聚合数据。您目前仅按 survey_question_id 分组。由于 ID 都不同，因此您永远不会在结果中得到汇总。

我建议将您的群组更改为：

GROUP BY survey_responders.province, survey_responses.questiontitle

并确保适当地编辑您的 SELECT 语句。

如何按两个不同的列对 MySQL 查询进行分组？

How do I group a MySQL query by two different columns?

mysql

group-by