我的 MySql 数据库中有以下表格:
+----------------------------------------------+
PROJECT
+----------------------------------------------|
+----------------------------------------------|
project_id | team_size | from_date
+----------------------------------------------|
1 | 34 | 1 Dec 2010
+----------------------------------------------|
2 | 2 | 2 Jan 1902
+----------------------------------------------|
3 | 99 | 15 Aug 1947
+----------------------------------------------+
+----------------------------------------------+
Technologies
+----------------------------------------------+
+----------------------------------------------+
technology_id | technology_name
+----------------------------------------------+
1 | Java
+----------------------------------------------+
2 | CPP
+----------------------------------------------+
3 | Hibernate
+----------------------------------------------+
4 | EJB
+----------------------------------------------+
5 | Python
+----------------------------------------------+
6 | Hadoop
+----------------------------------------------+
7424 | Perl
+----------------------------------------------+
要链接 Project 和 Technologies 表，我有下表:
+----------------------------------------------+
Project_Technologies
+----------------------------------------------+
+----------------------------------------------+
Project_ID | Technology_ID
+----------------------------------------------+
1 | 2
+----------------------------------------------+
1 | 7424
+----------------------------------------------+
2 | 1
+----------------------------------------------+
2 | 3
+----------------------------------------------+
2 | 4
+----------------------------------------------+
2 | 5
+----------------------------------------------+
我想在 UI 中以行和列的形式显示一个表中的数据。 例如:
+---------------------------------------------------+
project_id | team_size | from_date | technologies
|---------------------------------------------------|
| 1 | 34 | 1 Dec 2010| CPP, Perl |
|---------------------------------------------------|
| 2 | 2 | 2 Jan 1902| Java, Hibernate, EJB, Python |
|---------------------------------------------------|
| 3 | 99 |15 Aug 1947| |
+---------------------------------------------------+
我无法形成 sql 查询来得到这样的东西。我尝试了以下查询，它给了我重复的行。
select pr.project_id,pr.team_size,pr.from_date,tech.technology_name
from project pr, project_technologies ptech, technologies tl
where pr.project_id=ptech.project_id and ptech.technology_id=tl.technology_id
我想知道如何避免重复行？目前这个查询在 project_id=1 时给了我 2 行，在 project_id=2 时给了我 4 行
最佳答案
这应该可以解决问题......一个 group by 和一个 group_concat
select
pr.project_id,
pr.team_size,
pr.from_date,
GROUP_CONCAT(tech.technology_name separator ', ') as technologies
from
project pr
JOIN project_technologies ptech ON pr.project_id=ptech.project_id
JOIN technologies tl ON ptech.technology_id=tl.technology_id
GROUP BY
pr.project_id,
pr.team_size,
pr.from_date
编辑已修复以包含 JOIN 子句
关于mysql - 如何使用 SQL 合并来自多个表的数据？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/8061514/