Question

I have a database with two tables, Users and Posts. I’d like to write a php script to list, in order, the top 20 usernames with the number of posts they’ve made. The username field is cUsername in the Users table. The Users table intUserID field and the Posts table’s intPosterID field correspond to eachother.

Any help would be much appreciated. Thanks!

Answer 1

Use GROUP BY and count. This will get you a list of user IDs to their counts:

SELECT intPosterId, COUNT(*)
FROM Posts
GROUP BY intPosterId
ORDER BY COUNT(*) DESC
LIMIT 20

You can use the result in a subquery:

SELECT u.cUsername, pcnt.postCount
FROM Users AS u
INNER JOIN (
    SELECT intPosterId, COUNT(*) as postCount
    FROM Posts
    GROUP BY intPosterId
    ORDER BY COUNT(*) DESC
    LIMIT 20
) AS pcnt
ON u.intUserId = pcnt.intPosterId

To use it in a PHP script:

<?php
$sql = '
    SELECT u.cUsername, pcnt.postCount
    FROM Users AS u
    INNER JOIN (
        SELECT intPosterId, COUNT(*) as postCount
        FROM Posts
        GROUP BY intPosterId
        ORDER BY COUNT(*) DESC
        LIMIT 20
    ) AS pcnt
    ON u.intUserId = pcnt.intPosterId
';
$pdo = new PDO(
    'mysql:host=your_host;dbname=your_db', 
    'username', 
    'password',
    array(PDO::ATTR_ERRMODE=>PDO::ERRMODE_EXCEPTION)
);
$stmt = $pdo->prepare($sql);
$stmt->execute();

while ($row = $stmt->fetch(PDO::FETCH_ASSOC)) {
    echo "{$row['cUsername']}: {$row['postCount']} <br />\n";
}