Question

我有3个表：项目，类别和 projects_categories 。

我想获取项目名称，描述和类别，但每个项目可以有多个类别，因此我使用下一个查询获取重复内容：

SELECT projects.name, projects.description, categories.name
FROM projects
JOIN projects_categories ON projects.project_id = projects_categories.project_id
JOIN categories ON projects_categories.category_id = categories.category_id
WHERE projects.project_id = ?

我得到了这个：

++ name +++   ++ description ++    ++ name (category) ++
project1      bla bla bla          film
project1      bla bla bla          music

你可以看到我得到两行而不是一行

Answer 1

Group_concat是您要查找的标记：

SELECT projects.name, 
       projects.description, 
       group_concat(categories.name SEPARATOR ' ') as category_name
FROM projects
JOIN projects_categories 
  ON projects.project_id = projects_categories.project_id
JOIN categories 
  ON projects_categories.category_id = categories.category_id
WHERE projects.project_id = ?
group by projects.name, projects.description

Answer 2

您可以使用GROUP_CONCAT组合类别并返回一行。

SELECT projects.name, projects.description, GROUP_CONCAT(categories.name)
FROM projects
JOIN projects_categories ON projects.project_id = projects_categories.project_id
JOIN categories ON projects_categories.category_id = categories.category_id
WHERE projects.project_id = ?
GROUP BY projects.name, projects.description

如何使用JOIN并避免获取重复数据？

2 个答案: