mysql - JOIN 两个表，同时按索引分组并匹配多个外部 id

Question

我有以下 3 个表格：

对象：

ObjectID ObjectDescription
1        "first"
2        "second"

属性：

AttributeID AttributeDescription
1           "att1"
2           "att2"
3           "att3"
4           "att4"

属性链接：

AttributeID ObjectID
1           1
2           1
4           1

现在我的问题：我现在想选择一些属性并想知道哪个对象具有我所有选择的属性。我尝试了以下方法：

SELECT * FROM `objects` 
    INNER JOIN `attributelink` 
         ON `objects`.`ObjectID` = `attributelink`.`ObjectID`
    WHERE `attributelink`.`AttributeID` =1 AND `attributelink`.`AttributeID` =2  
GROUP BY `objects`.`ObjectID` 

这显然行不通，因为一行不能有 2 个 AttributeID，但我该如何归档呢？

Answer 1

attributelink对于要检查的每个选定属性，您必须在表上加入一次：

SELECT o.ObjectID
FROM objects o
INNER JOIN attributelink a1 ON o.ObjectID = a1.ObjectID AND a1.AttributeID = 1
INNER JOIN attributelink a2 ON o.ObjectID = a2.ObjectID AND a2.AttributeID = 2
GROUP BY o.ObjectID

您的测试数据并没有显示很多关于它是否有效，但是 FWIW，这里是 sqlfiddle。

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另一种方法是使用COUNT DISTINCTand HAVING( GROUP BYsqlfiddle )：

SELECT o.ObjectID
FROM objects o
INNER JOIN attributelink a ON o.ObjectID = a.ObjectID
WHERE a.AttributeID IN (1,2) --here you filter the rows on the attributes to test
GROUP BY o.ObjectID
HAVING COUNT(DISTINCT(a.AttributeID)) = 2 --# of attributes, means "having ALL"