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Asked: 2026-06-07T05:04:52+00:00

I wonder how the following could be solved with a mysql query, but don’t

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I wonder how the following could be solved with a mysql query, but don’t really know how to proceed

i have 3 tables (i will try to keep them simple)

          post

       id  | content 
           |
       1   | bla, bla..

          comment                          |                votes
                                           |
id | post_id | comment | date              |        id | comment_id | date 
                                           |           |            |
5  |    1    |  derp   | 2012-07-06        |        1  |     5      | 2012-07-07
6  |    1    |  nherp  | 2012-07-07        |        2  |     5      | 2012-07-08
7  |    1    |  yada   | 2012-07-08        |        3  |     5      | 2012-07-09
8  |    1    |  lala   | 2012-07-09        |        4  |     6      | 2012-07-10
                                           |        5  |     6      | 2012-07-11    
                                           |        6  |     7      | 2012-07-12
                                           |        7  |     8      | 2012-07-13
                                           |

they are tied to each other in this way

comment.post_id is a fk to post.id

votes.comment_id is a fk to comment.id

What i’m trying to discover is how many votes have been given to the entire post after each comment. Or in other words, how many votes have been given to entire post after the submission of each comment.
So, for this example case i presented, the result i was expecting would be the following table

                                      result

                  id | post_id | comment | date        | votes_after_submission
                     |         |         |             | 
                  5  |    1    |  derp   | 2012-07-06  |          7
                  6  |    1    |  nherp  | 2012-07-07  |          6
                  7  |    1    |  yada   | 2012-07-08  |          5
                  8  |    1    |  lala   | 2012-07-09  |          4

This is giving my brain a knot, i tried using the CASE keyword in the COUNT statement, but couldn´t actually make it work for this problem, can anyone give me some clues, or point me in the right direction or maybe just throw me some google keywords to search for as i didn´t find anything on this problem.

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1 Answer

  1. Editorial Team

    If I understand your question and example result correctly, try this:

    SELECT C.id,C.post_id,C.comment,C.date, 
       (SELECT COUNT(*)
        FROM votes AS V 
        WHERE V.date > C.date 
          AND V.comment_id IN (SELECT id FROM comment AS C2 
                               WHERE C2.post_id=C.post_id)) AS votes_after_submission
FROM comment AS C
ORDER BY C.post_id, C.date

    I’m not sure it’s the most efficient, but it works.

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