转置MySQL查询-需要将行分为列 [英] Transpose MySQL query - need rows into columns

问题描述

一个菜鸟MYSQL用户....我有一个简单的MySQL查询，该查询返回值，并使用GROUP_CONCAT函数:

a rookie MYSQL user .... I have a simple MySQL query that returns values, and uses the GROUP_CONCAT function:

SELECT Productid, Name, GROUP_CONCAT(value)
FROM search_export 
Group By Productid, Name;

Productid   Name                     GROUP_CONCAT(value)
666056542   Brand Name           Netgear
1054677552  Ethernet Technology  Gigabit Ethernet
665655662   Form Factor          Wall Mountable,Desktop
56565765    Media Type Supported     Twisted Pair

但是，我需要转置查询，以便它以单独的列而不是行的形式返回名称". MySQL完全可以做到这一点吗?

However, I need to transpose the query so it returns 'Name' as seperate columns, not a row. Is this possible at all with MySQL?

推荐答案

您需要执行PIVOT操作，MySQL本身不支持该操作(与某些其他RDBMS不同).

You need to perform a PIVOT operation, which is not supported natively in MySQL (unlike some other RDBMS).

您可以获得的最接近的方法是按照以下几行来构造SQL:

The closest you can get is to construct SQL along the following lines:

SELECT   ProductId,
         GROUP_CONCAT(IF(Name='Brand Name'          ,value,NULL))
           AS `Brand Name`,
         GROUP_CONCAT(IF(Name='Ethernet Technology' ,value,NULL))
           AS `Ethernet Technology`,
         GROUP_CONCAT(IF(Name='Form Factor'         ,value,NULL))
           AS `Form Factor`,
         GROUP_CONCAT(IF(Name='Media Type Supported',value,NULL))
           AS `Media Type Supported`
FROM     search_export
GROUP BY ProductId

如果可能的Name值是动态的，则可以根据以下结果以更高级的语言生成此类SQL:

If the possible Name values are dynamic, you could generate such SQL in a higher level language from the results of:

SELECT DISTINCT Name FROM search_export

实际上，甚至可以使用SQL本身:

Indeed, one could even use SQL itself:

SELECT CONCAT('
         SELECT   ProductId, ',
       GROUP_CONCAT('
                  GROUP_CONCAT(IF(Name=',QUOTE(Name),',value,NULL))
                    AS `',REPLACE(Name,'`','``'),'`'
       ), '
         FROM     search_export
         GROUP BY ProductId
       ')
INTO @sql
FROM (
  SELECT DISTINCT Name FROM search_export
) t;

PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

请注意，如果有许多不同的Name值，则可能需要增加

Note that if there are a lot of different Name values, you may need to increase group_concat_max_len from its default of 1KiB.

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