多对多标签有条件选择

Question

我有三个MySQL表格 - 文档，文档标签和多对多关系表（带有文档ID和标签ID）。

Document 
+------+ 
| id | 
+------+ 
| 1 | 
| 2 | 
| 3 | 
| 4 | 
+------+ 

DocumentToTag 
+------+------+ 
|idDoc |idTag | 
+------+------+ 
| 1 | 1 | 
| 1 | 2 | 
| 2 | 1 | 
| 2 | 3 | 
| 4 | 4 | 
+------+------+ 

Tag 
+------+-------+ 
| id | value | 
+------+-------+ 
| 1 |  2 | 
| 2 |  4 | 
| 3 |  8 | 
| 4 | 42 | 
+------+-------+ 

有必要使用具有特定值的2（或更多）标签获取文档。我们用下面的连接查询：

SELECT DISTINCTROW 
Document.id 

FROM Document 
LEFT JOIN DocumentToTag AS dt1 ON dt1.idDoc = Document.id 
LEFT JOIN Tag AS tag1 ON dt1.idTag = tag1.id 
LEFT JOIN DocumentToTag AS dt2 ON dt2.idDoc = Document.id 
LEFT JOIN Tag AS tag2 ON dt2.idTag = tag2.id 

WHERE tag1.value = 'someTagValue' 
AND tag2.value = 'someOtherTagValue' 

在这种情况下，我们需要做的很多连接，我们需要在条件添加尽可能多的标签。所以他们的查询应该由一些脚本动态地创建。有没有更优雅的方式来处理它？

Answer 1

试试这个：

SELECT 
Document.id 
FROM Document 
    JOIN DocumentToTag AS dt1 
     ON dt1.idDoc = Document.id 
    JOIN Tag AS t 
     ON dt1.idTag = t.id 
WHERE t.value IN ('tag1', 'tag2', 'tag3') -- you can dynamicaly generate this list 
GROUP BY Document.id 
HAVING COUNT(DISTINCT t.value) = 3 -- you can pass this as parameter 

Answer 2

你可以看这个

SELECT DISTINCT 
    Document.id 
    FROM Document 
LEFT JOIN DocumentToTag AS dt1 ON dt1.idDoc = Document.id 
LEFT JOIN Tag AS tag1 ON dt1.idTag = tag1.id 

WHERE tag1.value in ('someTagValue' ,'someOtherTagValue') 

DEMO HERE