<?php

$db = new PDO('mysql:host=localhost;dbname=enwiki_p', 'u2204', '');

$statement = $db->prepare('select page_id, page_namespace, page_title from enwiki_p.categorylinks
    inner join enwiki_p.page on page_id = cl_from
    where cl_to = :categoryname');

$pageIds = array();
$visitedCategories = array();

function recurse(PDOStatement $statement, $catName, $recurseCount = 0)
{
    global $pageIds, $visitedCategories;

    // skip already visited
    if(isset($visitedCategories[$catName])) return;

    $visitedCategories[$catName] = $catName;

    echo "$recurseCount : recursing into $catName" . PHP_EOL;

    $statement->execute(array('categoryname' => $catName));
    $data = $statement->fetchAll(PDO::FETCH_ASSOC);

    foreach ($data as $row) {
        if($row['page_namespace'] == 14)
        {
            recurse($statement, $row['page_title'], $recurseCount + 1);
        }

        $pageIds[$row['page_id']] = $row['page_id'];
    }
}

recurse($statement, 'Philosophy');

echo count($pageIds);