ORDER BY one ID when there are more of the same ID's in one table

Question

I have 4 tables:

1. Users
2. Forums
3. Discussies (discussions)
4. Forumberichten (messages)

The table Forumberichten (messages) contains the id's of the Discussion (discussions) table as a reference to reactions on a discussion. If there are 5 reactions to a discussion, there are 5 id's in the table with the same value.

How do I display an echo of one discussion of every different discussion with the latest reaction on it?

I've tried ORDER BY, DISTICT, GROUP BY and other things but I can't get it to work. I keep getting more outputs of the same discussion or one discussion with the original input and not the latest reaction to it.

<?php
// DISCUSSIES FORUM SCHRIJVEN

$sql="SELECT forumberichten.discussieid,forumberichten.datum,discussies.discussieid,discussies.titel,discussies.forumid,discussies.highlight,forums.forumid,forums.forumnaam,users.userid,users.userimage,users.username FROM forumberichten,discussies,forums,users WHERE forumberichten.discussieid=discussies.discussieid AND discussies.forumid=forums.forumid AND forumberichten.userid=users.userid AND forums.forumid=1  ORDER BY forumberichten.bericht_id DESC LIMIT 3";
    $result = $conn->query($sql) or die ("The query could not be completed. try again");
    if ($result->num_rows > 0) {

    echo "
    <br>
    <table id='forumschrijvenklein'>
    <tbody>
    <tr>
    <td bgcolor='#1E1E1E'></td>
    <td nowrap bgcolor='#1E1E1E'>&nbsp;</td>
    <td nowrap bgcolor='#1E1E1E' class='sterrenkleur'>Discussie</td>
    <td nowrap bgcolor='#1E1E1E' class='sterrenkleur'>Laatste reactie</td>
    <td nowrap bgcolor='#1E1E1E' class='sterrenkleur'>Datum</td>
    <td nowrap bgcolor='#1E1E1E' class='sterrenkleur'></td>
    </tr>
     ";

    // output data of each row
       while ($row = $result->fetch_assoc()) {

    echo" 
    <tr>";if ($row["highlight"] == '1') {
    echo " <td bgcolor='#FC6'></td>";
    } else {
    echo "<td bgcolor='#1E1E1E'></td>";
    }
    echo"
    <td nowrap bgcolor='#1E1E1E'>";if ($row["userimage"] == '') {
    echo "
    <a href='user.php? id=" . $row['userid'] . "'</a><img    src='Images/users/nopicture.png' alt='nopicture'  class='userimage-tooltip-small' title='".$row['username']."''></a>";
    } else {
    echo "<a href='user.php? id=" . $row['userid'] . "'</a><img src='Images/users/".$row['userimage']."' class='userimage-tooltip-small' title='".$row['username']."''></a>";
    }           
    echo"</td>
    <td bgcolor='#1E1E1E'><a href='discussie.php? id=" . $row['discussieid'] . "'>".$row["titel"]."</a></td>
    <td bgcolor='#1E1E1E'><a href='user.php? id=" . $row['userid'] . "'</a>".$row["username"]."</a></td>
    <td nowrap bgcolor='#1E1E1E'>"; echo date("d-m-y H:i",strtotime($row["datum"]));"
    ";
    echo"
    </td> 
    <td nowrap bgcolor='#1E1E1E'></td>
    </tr>
    ";
    }
    }
    echo " 
    <tr>
    <td bgcolor='#1E1E1E'>&nbsp;</td>
    <td bgcolor='#1E1E1E'>&nbsp;</td>
    <td bgcolor='#1E1E1E'><img src='Images/lijntransparant.png' width='315' height='2'></td>
    <td bgcolor='#1E1E1E'><img src='Images/lijntransparant.png' width='140' height='2'></td>
    <td bgcolor='#1E1E1E'>&nbsp;</td>
    <td bgcolor='#1E1E1E'>&nbsp;</td>
    </tr>
    </tbody>
    </table>
    ";  
    }
    ?>

I tried the following, but it still doesn't work...:

$sql = "SELECT * 
FROM (((forumberichten

JOIN discussies
ON discussies.discussieid = forumberichten.discussieid) 

JOIN users
ON users.userid = forumberichten.userid)

JOIN forums
ON forums.forumid=forumberichten.forumid)

GROUP BY discussies.discussieid 
HAVING forumberichten.forumid = 3 AND forumberichten.bericht_id = max(forumberichten.bericht_id) 
ORDER BY forumberichten.bericht_id DESC";

Answer 1

We want the newest post on each unique thread, we can do that by...

Using GROUP BY and HAVING .

SELECT * 
FROM Posts
JOIN Discussions
    on Discussions.discussion_id = Posts.discussion_id
GROUP BY Discussions.discussion_id
HAVING Posts.post_time = max(Posts.post_time)
ORDER BY Posts.post_time DESC

This is an example ! Make sure you use it to modify your own, it's quite simple though. I don't have a database to test this, but I am tested with my own data and different columns and it worked.

Note: This assumes that each Id is identical in both tables. It also assumes that post_time is some time value that increases the more recent the post is (ie SQL Timestamp).