Question

我有这些表的MySQL数据库：

表产品：

+-------------+
| id          |
+-------------+
| 1           |
| 2           |
+-------------+

table attribute_values：

+-------------+----------+-----------+
| product_id  | key      | value     |
+-------------+----------+-----------+
| 1           | title    | Orange    |
| 1           | code     | O125      |
| 2           | title    | Pizza     |
| 2           | code     | O138      |
+-------------+----------+-----------+

我有这个MySQL查询：

SELECT  products.id,
        MAX(CASE WHEN attribute_values.key = 'title' THEN attribute_values.value END) title,
        MAX(CASE WHEN attribute_values.key = 'code' THEN attribute_values.value END) code
FROM    products JOIN attribute_values ON products.id = attribute_values.product_id
GROUP   BY products.id;

使用此输出：

+-------------+----------+-----------+
| id          | title    | code      |
+-------------+----------+-----------+
| 1           | Orange   | 0125      |
| 2           | Pizza    | O138      |
+-------------+----------+-----------+

我希望脚本为attribute_values.key的每个不同值生成一列，而不显式指定键（在这种情况下为标题和代码）。

即。 pseudoscript：

SELECT  products.id
generate column foreach distinct attribute_values.key
FROM    products JOIN attribute_values ON products.id = attribute_values.product_id
GROUP   BY products.id;

这在MySQL中是否可行？

感谢您的任何努力：）

Answer 1

要为动态值生成动态数据透视表，您需要将动态sql编写为

set @sql = null;
select
  group_concat(distinct
    concat(
      'max(case when a.`key` = ''',
      a.`key`,
      ''' then value end) AS ',
      a.`key`
    )
  ) into @sql
from attribute_values a ;

set @sql = concat('select p.id, ', @sql, ' from products p
                  join attribute_values a on a.product_id = p.id
                  group by p.id
');

prepare stmt from @sql;
execute stmt;
deallocate prepare stmt;

http://sqlfiddle.com/#!9/2224f/1

MySQL：动态地行到列

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