Question

我在mysql数据库中有3个表，如下面的

表1：视频

id    name
1     one
2     two
3     three

表2：标签

id    name
1     stage=test
2     age=under18

表3：tags_to_items 其中tags_id = tags.id和item_id = videos.id

tag_id    item_id
1         1
2         2
2         1
1         3

此处item_id 1有2个标签。我想从videos表中选择tag_id=1和tag_id=2的所有记录。所以输出应该是video.id=1。

请提前帮助我这样做。

Answer 1

您真的不需要视频或加入任何查询。到目前为止做你需要的：

SELECT item_id as VIDEO_ID 
   SUM(CASE WHEN tag_id = 1 THEN 1 ELSE 0 END) as tag_1,
   SUM(CASE WHEN tag_id = 2 THEN 1 ELSE 0 END) as tag_2
FROM tags_to items
WHERE tag_id = 1 or tag_id = 2
GROUP BY VIDEO_ID
HAVING tag_1>0 AND tag_2>0

Answer 2

SELECT * FROM videos WHERE id IN (SELECT item_id FROM tags_to_items WHERE tag_id IN (1,2) )

Answer 3

你可以这样做：

            SELECT t1.tag_id, t1.item_id, t2.name AS tagName, t3.name AS videoName FROM tags_to_items AS t1

            LEFT JOIN tags AS t2 ON t1.tag_id=t2.id

            LEFT JOIN videos AS t3 ON t1.item_id=t3.id

            WHERE t1.tag_id IN (1,2)

自定义连接查询从3表获取记录

3 个答案: