mysql - Mysql Group_Concat 函数

Question

不了解如何使用 GROUP_CONCAT 函数，因为我的查询似乎重复了我实际上并不想要的值。

我有三张桌子：

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Content
------------------
cid | title
2334 | Lorem Ipsum

------------------
Organizers
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cid | name | sort
2334 | John Doe | 0

------------------
Participants
------------------
cid | name | sort
2334 | Jane Doe | 0
2334 | Bob Hope | 1
2334 | Bart Simpson | 2

我正在尝试编写一个将产生的查询：

cid | title | organizers | participants
2334 | Lorem Ipsum | John Doe | Jane Doe, Bob Hope, Bart Simpson

所以，我正在尝试使用 GROUP_CONCAT。但是，值正在重复，所以我不确定如何输出我正在寻找的结果？

SELECT GROUP_CONCAT(co.name) as organizers, 
GROUP_CONCAT(cp.name) FROM content n 
LEFT JOIN organizers co ON n.cid = co.cid 
LEFT JOIN participants cp ON n.cid = cp.cid 
WHERE n.cid = 2334

以上产生：

cid | title | organizers | participants
2334 | Lorem Ipsum | John Doe, John Doe, John Doe | Jane Doe, Bob Hope, Bart Simpson

Answer 1

select group_concat(distinct co.name)

详细信息： http: //dev.mysql.com/doc/refman/5.0/en/group-by-functions.html#function_group-concat

句法

GROUP_CONCAT([DISTINCT] expr [,expr ...]
[按 {unsigned_integer | 排序 col_name | 表达式}
[升序 | DESC] [,col_name ...]]
[分隔符 str_val])

Answer 2

SELECT n.cid, n.Title,
  GROUP_CONCAT(DISTINCT co.name ORDER BY co.sort) as organizers, 
  GROUP_CONCAT(cp.name ORDER BY cp.sort) 
FROM Content n 
LEFT JOIN Organizers co ON n.cid = co.cid 
LEFT JOIN Participants cp ON n.cid = cp.cid 
GROUP BY n.cid