Best way Selecting comments on multiple posts

I want to create a activity stream just like Google+ or Facebook.

My Problem is im really unsure whats the best way to query comments on multiple posts.

The easiest way is just selecting the comments in a loop, but this is really not the way i want to go.

Another possibility is joining them together.

SELECT c. *, p. *
FROM posts p
LEFT JOIN comments c ON p.post_id = c.post_id
WHERE so开发者_运维知识库mething = something

Or selecting them separately.

SELECT * FROM posts WHERE something = something

SELECT * FROM comments WHERE post_id = 1 OR post_id = 2 OR post_id = 3

Is there a better way to do that?

I'm sorry for my bad english.

Regards

Try this:

SELECT * FROM comments 
WHERE post_id IN (
    SELECT post_id FROM posts WHERE <condition>
)

Or, if you know the post_ids:

SELECT * FROM comments WHERE post_id IN (1, 2, 3)