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Asked: 2026-05-27T09:12:17+00:00

I have a script I wrote I while back for comments, but it is

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I have a script I wrote I while back for comments, but it is only single threaded. I would like it to be multi-threaded, but only as so a user can reply to a comment, not so a user can reply to a comment of a comment. So the threads would only be two deep.

Currently I store a comment_id against a user_id in my database.

The only way I can think of to do the multi threaded comments, is to have a parent field in the comments table. But if I do this then when I am selecting the comments with PHP, I will have to do another SELECT command to select the comments children (if any) for each comment. Seems like a lot of work on the database.

There has to be a better way. Any ideas on this? Or tutorials?

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1 Answer

  1. Editorial Team

    There are three (four) alternative possibilities:

    1. A recursive query to select all comments based on their parent ids. This is supported by many database products and the syntax depends on the database type. Check the docs for more info (search for ‘recursive’).

    2. If you store the article id in each (sub-)comment, you can just select all comments with the article id in one regular select query. You can use the parent ids to properly display the comments on the page under the right parent comment:

      SELECT * FROM comments WHERE article_id = :article_id

    3. If you only need two levels of comments, you can use an extended where to include both first level and second level comments:

      SELECT * FROM comments 
WHERE parent_id = :article_id
OR    parent_id IN (SELECT id FROM comments WHERE parent_id = :article_id)

    4. It is also possible to use union all to combine two queries that have the same columns, but since I assume that all data are from the same table, there is probably no need for it (see the extended where-clause above):

      SELECT * FROM comments WHERE parent_id = :article_id
UNION ALL
SELECT * FROM comments WHERE parent_id IN 
    (SELECT id FROM comments WHERE parent_id = :article_id)

    Personally, I would go for option 2 because it is simple (no exotic SQL construct required), efficient (1 query) and flexible (supports as many levels of comments as you like).

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