1

这是我的基本participants表（显示为关联数组）：

[id] => 1
[campaign_id] => 41
[firstname] => Jeff
[lastname] => Berube

在另一个名为 的表上participants_custom，我可以添加多个属于participants一行的自定义数据。像这样：

[id] => 51
[participant_id] => 1
[name] => textfield_bh423vjhgv
[data] => qwerty1

[id] => 52
[participant_id] => 1
[name] => textfield_IDRr2kzjZR59Xjw
[data] => qwerty2

[id] => 53
[participant_id] => 1
[name] => textfield_6kj5bhjjg
[data] => qwerty3

我目前正在制作一个join，但它将唯一的name,participant_id和添加data到我的行中。我想要的是我的查询返回如下内容：

[id] => 1
[campaign_id] => 41
[firstname] => Jeff
[lastname] => Berube
[textfield_bh423vjhgv] => qwerty1
[textfield_IDRr2kzjZR59Xjw] => qwerty2
[textfield_6kj5bhjjg] => qwerty3

其中行值name变成一列，并且value，它的值。我怎样才能做到？

我找到了 this和this，但没有成功。我正在寻找一种适合我情况的方法。谢谢你的帮助。

4

1 回答 1

2 
SELECT  a.ID,
        a.Campaign_ID,
        a.FirstName,
        a.LastName,
        MAX(CASE WHEN b.data = 'qwerty1' THEN b.Name END) qwerty1,
        MAX(CASE WHEN b.data = 'qwerty2' THEN b.Name END) qwerty2,
        MAX(CASE WHEN b.data = 'qwerty3' THEN b.Name END) qwerty3
FROM    Participants a
        INNER JOIN Participants_Custom b
            ON a.ID = b.Participant_ID
GROUP   BY  a.ID,
            a.Campaign_ID,
            a.FirstName,
            a.LastName

更新 1

由于 的值data是未知的，因此更倾向于使用动态 sql 。

SET @sql = NULL;
SELECT
  GROUP_CONCAT(DISTINCT
    CONCAT(
      'MAX(CASE WHEN b.data = ''',
      data,
      ''' THEN b.Name ELSE NULL END) AS ',
      CONCAT('`',data, '`')
    )
  ) INTO @sql
FROM Participants_Custom;

SET @sql = CONCAT('SELECT  a.ID,
                           a.Campaign_ID,
                           a.FirstName,
                           a.LastName,', @sql, 
                  'FROM     Participants a
                            INNER JOIN Participants_Custom b
                                ON a.ID = b.Participant_ID
                    GROUP   BY  a.ID,
                                a.Campaign_ID,
                                a.FirstName,
                                a.LastName');

PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
于 2013-04-12T17:34:01.567 回答