使用group_concat的查询只返回一行 [英] Query using group_concat is returning only one row

问题描述

这是一个查询，它应该获取用户的信息，项目的信息，以及与此项目关联的所有图像路径的group_concat。

This is a query that is supposed to get the user's information, their project's information, and a group_concat of all the image paths that such project is associated to. To add to this, I am only getting the information mentioned from the people the user is following.

但是，只能重新调整一行。

This is, however, only retunring one row.

SELECT users.first_name, users.last_name, users.user_id, projects.project_id, projects.project_name, projects.project_time, group_concat(images.image_path)
FROM users, projects, images
WHERE users.user_id = projects.user_id
AND users.user_id IN (SELECT follow_user_2 FROM following WHERE follow_user_1 = 1)
 ORDER BY projects.project_id DESC

TO COMPARE： WORKS 意味着在循环中，它会提供所有用户的信息和与此类用户相关的项目信息。

TO COMPARE: The following query WORKS in the sense that in the loop it gives all of the user's information and the projects information related to such user.

SELECT users.first_name, users.last_name, users.user_id, projects.project_id, projects.project_name, projects.project_time 
    FROM users, projects
    WHERE users.user_id = projects.user_id 
    AND users.user_id IN (SELECT follow_user_2 FROM following WHERE follow_user_1 = 1)
    ORDER BY projects.project_id DESC

当我尝试使用group_concat时，它只返回一个行，我不明白为什么。

When I try to use group_concat it just returns me one row and I do not understand why.

请帮帮我？谢谢。如果我的问题不够清楚，我会详细说明。

Can someone help me please? Thank you. If my question was not clear enough, I will elaborate.

如果这有帮助，这里是一个SQL FIDDLE。
http://www.sqlfiddle.com/#!2/867f6/2
我不得不缩短我的架构很多。

If this helps, here's an SQL FIDDLE. http://www.sqlfiddle.com/#!2/867f6/2 I had to shorten my schema a lot. Try both queries to above to see the problem.

推荐答案

当我尝试使用group_concat时返回一行，我不明白为什么。

When I try to use group_concat it just returns me one row and I do not understand why.

因为你没有使用 GROUP BY 子句。当使用 GROUP_CONCAT 的聚合函数时，您需要告诉数据库您希望数据合并的列。

Because you have not used the GROUP BY clause in your query. When using aggregate functions like GROUP_CONCAT you need to tell the database about the column using which you want your data to be combined.

目前，您的查询会对所有记录进行分组，并在输出中提供1条记录。

Currently your query is grouping all records and giving 1 record in the output.

如果添加 GROUP BY users.userid 在查询，然后记录将按唯一userid的组。我更新了你的小提琴，它现在给了2条记录： http://www.sqlfiddle.com/#!2/867f6 / 18>

If you add GROUP BY users.userid in the query then the records will be grouped by unique userid's. I updated your fiddle and it now gives 2 records: http://www.sqlfiddle.com/#!2/867f6/18

请注意：在标准SQL查询中，GROUP BY子句中列出的列应与SELECT子句中的列匹配（聚合函数除外） 。

Please note: In standard SQL queries, columns listed in the GROUP BY clause should match the column in the SELECT clause (except the aggregate functions).

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