旋转 mysql table 不起作用

Question

我已经阅读了 artfulsoftware 和这里的许多主题，但仍然不明白为什么我不能让它工作。

我有一个非常简单的 table (productProperties pp) 三列：

prodName propName propValue

我要查询所以它会表示为（例如）

prodName Color  Weight Adhesive
nail1    black  1lbs   3m 
nail2    silver 0.5lbs 3m

我尝试了什么：

select 
    pp.prodName,
     CASE pp.propName
        WHEN 'Color' THEN pp.propValue
        ELSE NULL
    END as 'Color',

   CASE pp.propName
        WHEN 'Weight' THEN pp.propValue
        ELSE NULL
    END as 'Weight',

   CASE pp.propName
        WHEN 'Adhesive' THEN pp.propValue
        ELSE NULL
    END as 'Adhesive'      
from
    ProductsProperties as pp    
group by pp.prodName;

除了 prodName

，我得到的都是 NULL

例如：

prodName propName   propValue
nail1    Color      black
nail1    Adhesive   3M
nail2    Weight     1lbs
nail3    Color      black
nail3    Adhesive   3M
nail5    Weight     1lbs

以上查询结果为：

 prodName, Color,   Weight, Adhesive
 nail1,    black,   NULL,   NULL
 nail2,    NULL,    1lbs,   NULL
 nail3,    black,   NULL,   NULL
 nail5,    NULL,    1lbs,   NULL

Answer 1

您需要将 CASE 包装成 GROUP_CONCAT():

SELECT
    pp.prodName,
    GROUP_CONCAT(DISTINCT CASE pp.propName
        WHEN 'Color' THEN pp.propValue
        ELSE NULL
    END) AS'Color',

    GROUP_CONCAT(DISTINCT CASE pp.propName
        WHEN 'Weight' THEN pp.propValue
        ELSE NULL
    END) AS 'Weight',

    GROUP_CONCAT(DISTINCT CASE pp.propName
        WHEN 'Adhesive' THEN pp.propValue
        ELSE NULL
    END) AS 'Adhesive'      
FROM
    ProductsProperties AS pp    
GROUP BY pp.prodName;

Answer 2

使用join的解决方案：

select distinct pp1.prodName, 
       pp2.propValue as 'Color', 
       pp3.propValue as 'Adhesive', 
       pp4.propValue as 'Weight' 
from ProductsProperties pp1 
  left join ProductsProperties pp2 on pp1.prodName = pp2.prodName and pp2.propName = 'Color'
  left join ProductsProperties pp3 on pp1.prodName = pp3.prodName and pp3.propName = 'Adhesive'
  left join ProductsProperties pp4 on pp1.prodName = pp4.prodName and pp4.propName = 'Weight';

旋转 mysql table 不起作用

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