我从这样的选择输出：
04:47:37> select * from attributes left outer join trailer_attributes on attributes.id = trailer_attributes.attribute_id; +----+--------------+----------+-----------+------------+--------------+-----------------+ | id | name | datatype | list_page | trailer_id | attribute_id | attribute_value | +----+--------------+----------+-----------+------------+--------------+-----------------+ | 1 | Make | text | 1 | 1 | 1 | Apple | | 1 | Make | text | 1 | 2 | 1 | sdfg | | 2 | Year | number | 1 | 1 | 2 | 2009 | | 2 | Year | number | 1 | 2 | 2 | sdfg | | 3 | Type | text | 0 | 1 | 3 | iPhone | | 3 | Type | text | 0 | 2 | 3 | sdfg | | 4 | Axles | text | 0 | 1 | 4 | asdf | | 4 | Axles | text | 0 | 2 | 4 | sdfg | | 7 | Size | text | 0 | 1 | 7 | asd1 | | 7 | Size | text | 0 | 2 | 7 | sdfg | | 8 | Frame | text | 0 | 1 | 8 | | | 8 | Frame | text | 0 | 2 | 8 | sdfg | | 9 | Height | text | 0 | 1 | 9 | | | 9 | Height | text | 0 | 2 | 9 | sdfg | | 10 | Dollies | text | 0 | 1 | 10 | | | 10 | Dollies | text | 0 | 2 | 10 | sdfg | | 11 | Tires/Wheels | text | 0 | 1 | 11 | | | 11 | Tires/Wheels | text | 0 | 2 | 11 | sdfg | | 12 | Condition | text | 1 | 1 | 12 | New | | 12 | Condition | text | 1 | 2 | 12 | sdfg | | 13 | Title | text | 0 | 1 | 13 | | | 13 | Title | text | 0 | 2 | 13 | sdfg | +----+--------------+----------+-----------+------------+--------------+-----------------+
我想将其转换为以下内容：
id, Make, Year, Type, Axles, Size, Frame (etc) 1, Apple, 2009, iPhone, ..... 2, sdfg, sdfg, sdfg, .....
有什么建议？
嗯… EAV。避免使用EAV（entity- attribute_value）的许多原因之一是，它们更难以报告和查询。但是，如果提前知道所需的属性，则可以执行以下操作：
Select id , Min( Case When name = 'Make' Then attribute_value End ) As Make , Min( Case When name = 'Year' Then attribute_value End ) As Year , Min( Case When name = 'Type' Then attribute_value End ) As Type , Min( Case When name = 'Axles' Then attribute_value End ) As Axles , Min( Case When name = 'Size' Then attribute_value End ) As Size , Min( Case When name = 'Frame' Then attribute_value End ) As Frame , ... From attributes Where name In('Make','Year','Type','Axles','Size','Frame',....) Group By id
现在，MySQL确实具有GROUP_CONCAT，如果允许的话，它可以让您将同一属性的多个值连接到一个列表中（例如，如果一个实体可以具有多个Make属性）。
