MySQL query for a many-to-many relationship table

Question

i have some problems here and i need help.

I have a table called , another table called and many-to-many relationship between them called 的表，另一个名为表，它们之间的多对多关系称为

Here is the strucutre:

• id
• title
• description

• id
• name
• seo

• id
• post_id
• tag_id

So let's say now i want to build a query to match multiple tags by having their tag_id already. For an example let's try to match all posts which has tag_id 11, tag_id 133 and tag_id 182. What i could do was selecting them with OR operator but these are not the results i want because what i want is to match all posts which has all mentioned tags only not just if contains some...

My query was:

SELECT * FROM item_tags WHERE tag_id='11' OR tag_id='133' OR tag_id='182'

Which is wrong...

Here is a screenshot of the table: https://i.imgur.com/X60HIM5.png

PS: I want to build a search based on multiple keywords (tags).

Thank you!

Answer 1

If you want all posts that have been tagged with all three tags, then you could use:

select p.*
from posts p
where exists (select 1 from item_tags a where a.post_id = p.id and a.tag_id = 11)
  and exists (select 1 from item_tags a where a.post_id = p.id and a.tag_id = 133)
  and exists (select 1 from item_tags a where a.post_id = p.id and a.tag_id = 182)

If you want posts tagged with any of those three tags use:

select p.*
from posts p
where exists (select 1 from item_tags a where a.post_id = p.id and a.tag_id = 11)
   or exists (select 1 from item_tags a where a.post_id = p.id and a.tag_id = 133)
   or exists (select 1 from item_tags a where a.post_id = p.id and a.tag_id = 182)

Answer 2

重要说明：我尚未测试！

SELECT * FROM posts WHERE id IN(SELECT post_id FROM item_tags WHERE item_tags.tag_id='11' OR item_tags.tag_id='133' OR item_tags.tag_id='182');

Answer 3

You can group result by post_id and then save only those having all tags linked

select * 
from posts 
where id in (
    select post_id 
    from item_tags 
    where tag_id in (11,133,182) 
    group by post_id 
    having count(tag_id)=3
)