SQL GELO

SELECT
    topic_id,
    topic_subject,
    user_name,
    topic_date,
    (select user_name from users, posts where post_by=user_id and post_topic= 'catid' ORDER BY post_date DESC LIMIT 1) AS 'Last Poster',
    (select post_date from users, posts where post_by=user_id and post_topic= 'catid' ORDER BY post_date DESC LIMIT 1) AS 'Last Time'

FROM
    users, topics

WHERE
    cat_id = 'catid' AND users.user_id = topics.topic_by