Data structure, best practice to build true "related by tags" items list?

What I mean saying true "related by tags" list?

Let's imagine that article have 3 tags: A, B, C. True "related by tags" articles for this item will be articles fistly having A, B, C tags, then (A, B), (A, C), (B, C) etc.

table: tags

tag_id
tag_title
tag_nicetitle

table: tags2articles

article_id
tag_id

Using this tables structure is too difficult to calculate true "related by tags".

We can add one more table containing article_id and it's md5(A,B,C). Before hashing we should sort tags by alphabet.

table: article_tags_hashed

id
article_id
md5
count

This table will help us to find articles containing exact set of tags (A,B,C), but it won't help to find art开发者_开发知识库icles containing only (A, B), (A, C), (B, C)

What is the best practice?

PS: Sorry for my english, it's pretty bad.

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I don't think you need article_tags_hashed because you can group and count the results when you
query the tags2articles.

Example:

select article_id, count(article_id) as tagcnt from tags2articles
where tag_id in (...)
group by article_id
order by tagcnt desc

The articles which contain the most tags will be placed first.