自定义联接查询以从3个表中获取记录

Question

I have 3 table in mysql database like following

id    name
1     one
2     two
3     three

id    name
1     stage=test
2     age=under18

where tags_id = tags.id and item_id = videos.id

tag_id    item_id
1         1
2         2
2         1
1         3 

Here item_id 1 has 2 tags. I want to select all the records from videos table where tag_id=1 and tag_id=2 . So output should be video.id=1 .

Please help me to do like that, thanks in advance.

Answer 1

You really don't need any query from videos or join. Just do what you need so far:

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

You can do like this:

            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)