Question

我有3个表和testdata，见下文。

如何让这个输出进行查询？

Itemname     Name        Address
========================================
Test Item 1  test name 1 test address 1
Test Item 2  test name 2 test address 2

表Item：

id   Name
========================================
1 - Test Item 1
2 - Test Item 2

表Itemproperties：

id item_id property_id value
======================================
1  1       1           test name 1
1  1       2           test address 1
1  2       1           test name 2
1  2       2           test address 2

表Properties：

id name
===========
1  name
2  address

Answer 1

您需要两次加入Itemproperties表，一次是名称，一次是地址：

SELECT
  i.name Itemname,
  ip1.value Name,
  ip2.value Address
FROM
  Item i
  JOIN Itemproperties ip1 ON i.id = ip1.item_id AND ip1.property_id = 1
  JOIN Itemproperties ip2 ON i.id = ip2.item_id AND ip2.property_id = 2

Answer 2

一种方法是对名称和地址进行硬编码。

SELECT I.Itemname,IPN.value AS Name, IPA.value AS Address
FROM Item I
LEFT JOIN Itemproperties IPN
ON IPN.item_id=I.id
LEFT JOIN Itemproperties IPA
ON IPA.item_id=I.id
WHERE IPN.property_id=1 AND IPA.property_id=2

MySQL Query具有属性和内部联接

2 个答案: