Question

I’m developing a blog system with php and mysql with the following db structure:

Article
   -id
   -firstMessage
   -lastMessage
   -body

Comment
   - id
   - article_id
   - publiched_date
   - body

The idea here is make use of pagination, where the article with a lot of comments shows a link tree like [first][1][2][3][last], 10 comments by page. Everything goes fine, I have create a nice sql that select 10 messages according to the page number by url:

example.com/?article=3&page=2

Where is the ploblem? Well, supponse that I have this url in my homepage:

example.com/?article=3&message=3565

According to the url above, How can I determinate the page number where this message is? Do you have any idea to guide me to the right direction?

Edit

• The messages ids are not consecutives, for example, an article could have the comments: 125, 364, 561, 1522

Answer 1

Basically, select the comments from the same article, sorted by ID (or another column if the id can be out of order–non-consecutive is fine), and do a little math with the result. Here’s the code (demo):

SELECT (
  SELECT CEILING((count(*) + 1) / 10)
  FROM `Comment`
  WHERE `id` < `comment`.`id`
  AND `article_id` = `comment`.`article_id`
) AS `page`
FROM `Comment`
WHERE `id` = ?
AND `article_id` = ?

Simply plug in the comment ID and article ID where the ? are (or, even better, use this exact code in a prepared statement). If you change the number of comments per page, make sure you change the 10 in the query as well.

For this query, you just need an index on article_id (and a PRIMARY index on id).