Question

这是我的基本participants表（显示为关联数组）：

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

在名为participants_custom的另一个表上，我可以添加属于participants行的多个自定义数据。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join，但它会将name，participant_id和data添加到我的行中。我想要的是我的查询返回这样的内容：

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

行值name成为列，value，它是值。 我该怎么做？

我找到了this和this，但未成功。我找到了一种适合我情况的方法。谢谢你的帮助。

Answer 1

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

SQLFiddle Demo

更新1

由于data的值未知，因此首选动态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;

SQLFiddle Demo

MySQL选择特定的行值作为列名

1 个答案: