How to select more than 2 matches?

I'm having trouble thinking this one out. Input is greatly appreciated. Content is always changing, but here is an example of what I'm trying to do.

STORY 1 (keywords: 5, 9, 17, 18, 25, 22)

STORY 2 (keywords: 5, 25, 16, 19, 32)

STORY 3 (keywords: 1, 9, 1开发者_StackOverflow中文版7)

STORY 4 (keywords: 25, 22, 16, 3, 17)

Now, I'm querying based on STORY 1. I'd like to output any stories that share >= 2 keywords with STORY 1.

For this example, my code should output:

STORY 1

STORY 2

STORY 4

STORY 2 shares keywords 5, 25

STORY 4 shares keywords 25, 22, 17

STORY 3 is not outputted simply because it only shares 1 keyword with STORY 1

Any ideas?

Something like (not tested)

SELECT k2.story_id
FROM keywords k1 
     JOIN keywords ks ON k1.keyword = k2.keyword AND k1.story_id < k2.story_id
GROUP BY 
     k1.story_id
WHERE 
     k1.story_id = @story_id
HAVING COUNT(*) > 1

might work for you.

You can do it from SQL as Unreason showed, it is also very easy to do from PHP. Just make every Story an array of keywords and use array_intersect(story_1, story_n). You keep result arrays having more than two items.