MySQL动态地从行中创建列

我的问题是我有一个表

apidata

，它为每个域保存多行数据。因此，当我查询

apidata

时，自然会得到多行结果。有没有办法把这些行变成列？我这样问是因为我已经在使用一个查询来提取域数据（页面标题、URL、顶级域、ip地址等），我需要添加api数据。我相信我必须在两个查询中完成这项工作，但我希望每个域至少有一行，以使查询和循环尽可能快

所以问题是，我可以用行动态创建列吗？

这里有一个SQL Fiddle=>

（注意，我没有把整个数据库放在小提琴上，只是放在影响查询的表上。如果您认为缺少一些您需要的东西，请告诉我。）

工具运行（id\u sha是工具运行的主要查找值）

域（Run\u id对于tool\u runs.id是FK）

API数据

| ID | DOMAIN_ID | EXPORT_COLUMN    | COLUMN_TITLE      | VALUE |
+----+-----------+------------------+-------------------+-------+
| 1  | 1         | referringDomains | Referring Domains | 10    |
+----+-----------+------------------+-------------------+-------+
| 2  | 1         | linkCount        | Backlink Count    | 55    |

下面是我的问题：

SELECT a.domain_id, a.export_column, a.column_title, a.value 
FROM apidata AS a WHERE domain_id IN
(
  SELECT d.id FROM tool_runs AS t
  JOIN domains AS d ON d.run_id = t.id
  WHERE id_sha = '68300DF58B2A8A6E098CB0B3D1A9AE80BBE5897A'
)
ORDER BY a.domain_id

我得到的是：

| DOMAIN_ID | EXPORT_COLUMN    | COLUMN_TITLE      | VALUE    |
+-----------+------------------+-------------------+----------+
| 1         | referringDomains | Referring Domains | 10       |
+-----------+------------------+-------------------+----------+
| 1         | linkCount        | Backlink Count    | 55       |

但我想要的是

| DOMAIN_ID | referringDomains | referringDomains_TITLE | linkCount | linkCount_TITLE |
+-----------+------------------+------------------------+-----------+-----------------+
| 1         | 10               | Referring Domains      | 55        | Backlink Count  |

---

您尝试的是将表的行透视到列中。不幸的是，MySQL没有本机pivot表运算符，但您可以使用

CASE

表达式来执行此操作：

SELECT 
  a.Domain_id,
  MAX(CASE WHEN a.export_column = 'referringDomains' THEN a.value END) AS referringDomains,
  MAX(CASE WHEN a.export_column = 'referringDomains' THEN a.column_title END) AS referringDomains_TITLE,
  MAX(CASE WHEN a.export_column = 'linkCount' THEN a.value END) AS linkCount,
  MAX(CASE WHEN a.export_column = 'linkCount' THEN a.column_title END) AS linkCount_TITLE
FROM apidata AS a 
WHERE domain_id IN
(
  SELECT d.id FROM tool_runs AS t
  JOIN domains AS d ON d.run_id = t.id
  WHERE id_sha = '68300DF58B2A8A6E098CB0B3D1A9AE80BBE5897A'
) 
GROUP BY a.domain_id;

---

请注意：如果要对

export\u列中的所有值执行此操作，必须为每个值编写一个
大小写表达式。但您可以使用动态sql这样做：

SET @ecvalues = NULL;
SET @ectitles = NULL;
SET @sql = NULL;

SELECT
  GROUP_CONCAT(DISTINCT CONCAT('MAX(IF(a.export_column = ''',
      a.export_column, ''', a.value , NULL)) AS ', '''', a.export_column , '''')
  ) INTO @ecvalues
FROM apidata a;


SELECT
  GROUP_CONCAT(DISTINCT CONCAT('MAX(IF(a.export_column = ''',
      a.export_column, ''', column_title , NULL)) AS ', '''', CONCAT(a.export_column , '_Titles'), '''')
  ) INTO @ectitles
FROM apidata a;


SET @sql = CONCAT('SELECT 
  a.Domain_id, ', @ectitles , ',', @ecvalues, '
    FROM apidata AS a 
WHERE domain_id IN
(
  SELECT d.id FROM tool_runs AS t
  JOIN domains AS d ON d.run_id = t.id
  WHERE id_sha = ''68300DF58B2A8A6E098CB0B3D1A9AE80BBE5897A''
) 
GROUP BY a.domain_id;');

prepare stmt 
FROM @sql;

execute stmt;

可以将该查询放入存储过程中



作为@MahmoudGamal答案的补充，您应该知道，对于任何新的注册表（
EXPORT\u COLUMN
），您必须添加一个新的
case
语句

因此，为了实现动态，您可以在dba.stackexchange上创建一个过程，如本文所述


它显示了如何动态执行此操作。
如果您想要列，请按照上面的示例继续并旋转。如果出于某种报告原因，您只需要一个字符串，请继续执行以下操作：

SELECT group_concat(CONCAT_WS(' ',a.domain_id, a.value, a.column_title, a.export_column, 'next row string separator'))
FROM apidata AS a WHERE domain_id IN
(
  SELECT d.id FROM tool_runs AS t
  JOIN domains AS d ON d.run_id = t.id
  WHERE id_sha = '68300DF58B2A8A6E098CB0B3D1A9AE80BBE5897A'
)
ORDER BY a.domain_id

除了答案，仅供参考Rachel，技术术语是数据透视或数据透视表，以备进一步研究。MySQL还有
IF（）
函数，它比单个条件'case'语句稍微简单一点。@fancyPants谢谢你，我确实想研究一下，因为它会很方便：）一般来说，出于灵活性和可伸缩性的考虑，最好在应用程序级别处理数据显示问题——假设您有一个（例如，一个简单的PHP循环作用于一个有序数组）
SET @ecvalues = NULL;
SET @ectitles = NULL;
SET @sql = NULL;

SELECT
  GROUP_CONCAT(DISTINCT CONCAT('MAX(IF(a.export_column = ''',
      a.export_column, ''', a.value , NULL)) AS ', '''', a.export_column , '''')
  ) INTO @ecvalues
FROM apidata a;


SELECT
  GROUP_CONCAT(DISTINCT CONCAT('MAX(IF(a.export_column = ''',
      a.export_column, ''', column_title , NULL)) AS ', '''', CONCAT(a.export_column , '_Titles'), '''')
  ) INTO @ectitles
FROM apidata a;


SET @sql = CONCAT('SELECT 
  a.Domain_id, ', @ectitles , ',', @ecvalues, '
    FROM apidata AS a 
WHERE domain_id IN
(
  SELECT d.id FROM tool_runs AS t
  JOIN domains AS d ON d.run_id = t.id
  WHERE id_sha = ''68300DF58B2A8A6E098CB0B3D1A9AE80BBE5897A''
) 
GROUP BY a.domain_id;');

prepare stmt 
FROM @sql;

execute stmt;

SELECT group_concat(CONCAT_WS(' ',a.domain_id, a.value, a.column_title, a.export_column, 'next row string separator'))
FROM apidata AS a WHERE domain_id IN
(
  SELECT d.id FROM tool_runs AS t
  JOIN domains AS d ON d.run_id = t.id
  WHERE id_sha = '68300DF58B2A8A6E098CB0B3D1A9AE80BBE5897A'
)
ORDER BY a.domain_id