Question

I want to create something like reddit where they have comments, then replies to the comment, then reply to the reply.

What type of database structure do they use so:

1. they keep track of all the comments to a posting
2. a reply to a comment
3. a reply to a reply

All I have right are is just a posting and a bunch of comments relating to it like..

POSTING TABLE
posting_id | title | author

COMMENTS TABLE
comment_id | posting_id | comment

REPLIES TABLE
????

How do I relate the comments to the replies?
What type of css do they use to give replies that indented space?

EDIT:
Thanks for the answers! Now my only question how do I indent the replies?
Such as..

you like food
     yes I love italian
        Yes i do like it too
     chinese is best

Answer 1

You can add another column to your comments table specifying parent_comment_id where you populate it with the ID of the comment (or reply) the user is replying to. In the case where the comment is a direct reply to the post (not a reply to a comment) this column would be null.