转换 MySQL 个表

Question

我有一个 MySQL table，其布局如下所示：

---------------------------------------
| ID | TITLE       | VALUE  | PART NO |
---------------------------------------
| 1  | width (mm)  | 12     |    234  |
---------------------------------------
| 2  | colour      | red    |    234  |
--------------------------------------- 
| 3  | colour      | blue   |    235  |
---------------------------------------
| 4  | width (mm)  | 2      |    234  |
---------------------------------------  
| 5  | Part No.    | 235    |    235  |
---------------------------------------
| 6  | Part No.    | 234    |    234  |
---------------------------------------

我希望 table 看起来像这样：

----------------------------------------
| id  | Width (mm) | colour | Part No. |
----------------------------------------
| 1   | 12         | red    |   234    |
----------------------------------------
| 2   | 2          | blue   |   235    |
----------------------------------------

我找到了另一个答案，但后来丢失了 link - 这个答案没有解决我的问题，因为它只适用于数字。

我需要 SQL 代码来说明标题中的 ( 和值中的单词（不仅仅是添加数字）。

我使用找到并丢失的答案创建了下面的 SQL - 它有点工作，但我缺少大量数据 returns "Manufacturer" 列和第一个 "Alternative Partnumber" 列，但没有别的。（这让我感到困惑 - table 中有 weight 和 Height 100% 并且这两个字段在查询中彼此不接近。）

SQL代码

SELECT 
    part_number,
    part_number AS pn, 
        if( title = 'Alternative Partnumber', (SELECT table_name.value FROM `table_name` WHERE table_name.part_number = pn AND table_name.title = 'Alternative Partnumber'), '' ) AS `Alternative Partnumber`,
        if( title = 'Amp', (SELECT table_name.value FROM `table_name` WHERE table_name.part_number = pn AND table_name.title = 'Amp'), '' ) AS `Amp`,
        if( title = 'Amp Rating (Constant Torque)', (SELECT table_name.value FROM `table_name` WHERE table_name.part_number = pn AND table_name.title = "Amp Rating (Constant Torque)"), '' ) AS `Amp Rating (Constant Torque)`,
        if( title = 'Analogue Inputs', (SELECT table_name.value FROM `table_name` WHERE table_name.part_number = pn AND table_name.title = "Analogue Inputs"), '' ) AS "Analogue Inputs",
        if( title = 'Analogue output', (SELECT table_name.value FROM `table_name` WHERE table_name.part_number = pn AND table_name.title = "Analogue output"), '' ) AS "Analogue output",
        if( title = 'Manufacturer', (SELECT table_name.value FROM `table_name` WHERE table_name.part_number = pn AND table_name.title = 'Manufacturer'), '' ) AS `Manufacturer`, 
        if( title = 'Weight', (SELECT table_name.value FROM `table_name` WHERE table_name.part_number = pn AND table_name.title = 'Weight'), '' ) AS `Weight`,
        if( title = 'Width', (SELECT table_name.value FROM `table_name` WHERE table_name.part_number = pn AND table_name.title = 'Width'), '' ) AS `Width`,
        if( title = 'Width (mm)', (SELECT table_name.value FROM `table_name` WHERE table_name.part_number = pn AND table_name.title = 'Width (mm)'), '' ) AS `Width (mm)`
FROM 
    table_name 
GROUP BY 
    part_number;

我需要另一个 SQL 来进行分组吗？我认为那是它丢失数据的地方。

谢谢，瑞安

Answer 1

您可以进行条件聚合来调整 EAV 模型，如下所示：

select 
    min(id) id,
    max(case when title = 'width (mm)' then value end) width_mm,
    max(case when title = 'color' then value end) colour,
    part_number
from mytable
group by part_number

转换 MySQL 个表

Converting MySQL Tables

mysql

sql

pivot

group-by

entity-attribute-value