mysql - 我们可以对 group_concat(distinct somefield) 做一个 DISTINCT 吗？

Question

http://sqlfiddle.com/#!2/37dd94/17

如果我执行 SELECT DISTINCT，我得到的结果与只执行 SELECT 的结果相同。

在查询结果中，您将看到两个包含 District“Evora”的事件。应该只出现一个。

有什么线索吗？

Answer 1

下面的查询 (SQL FIDDLE) 怎么样:

SELECT GROUP_CONCAT(APA_T.district), t.name
FROM tbl_activity AS t 
JOIN tbl_activity_package AS ap ON t.id = ap.id_activity 
JOIN 
(
  SELECT DISTINCT apa.district AS district, 
  (
     SELECT s1.id_activity_package 
     FROM tbl_activity_package_address s1
     WHERE apa.district = s1.district
     ORDER BY s1.id DESC
     LIMIT 1
  ) AS idActivityPackage
  FROM 
  tbl_activity_package_address apa
  ORDER BY apa.district
) AS APA_T
ON ap.id = APA_T.idActivityPackage
GROUP BY t.name 
ORDER BY APA_T.district;

上述查询将消除多余的Faro 和Evora。