多对多标签条件选择

Question

我有三个MySQL表- documents、document标签和多对多关系表(带有文档ids和标签ids )。

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 |
+------+-------+

有必要获取具有例如2个(或更多)具有特定值的标签的文档。我们使用以下连接查询：

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，我们需要在条件中添加尽可能多的连接和标签。因此它们查询应该由某个脚本动态创建。有没有更优雅的方法来处理它？

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')