The query used for the Forum List view does a simple join of tf and mf. Hence, if there are no messages for a forum topic, the forum topic count is 0.
I think the right fix is to replace the following query with a LEFT JOIN as follows.
I tested by taking the query from the DEBUG log (before) and changing the simple join on tf,mf to a LEFT JOIN (after). I used sqlite3 interface to confirm desired results
before:
SELECT f.id, f.name, f.author, f.time, f.moderators, f.forum_group, f.subject, f.description, tm.topics, tm.replies, tm.lastreply, tm.lasttopic FROM forum f LEFT JOIN ( SELECT tf.forum AS forum, topics, lasttopic, replies, lastreply FROM (SELECT COUNT(id) AS topics, MAX(time) AS lasttopic, forum FROM topic GROUP BY forum) tf, (SELECT COUNT(id) AS replies, MAX(time) AS lastreply, forum FROM message GROUP BY forum) mf WHERE tf.forum = mf.forum) tm ON f.id = tm.forum ORDER BY f.id ASC;
after:
SELECT f.id, f.name, f.author, f.time, f.moderators, f.forum_group, f.subject, f.description, tm.topics, tm.replies, tm.lastreply, tm.lasttopic FROM forum f LEFT JOIN ( SELECT tf.forum AS forum, topics, lasttopic, replies, lastreply FROM (SELECT COUNT(id) AS topics, MAX(time) AS lasttopic, forum FROM topic GROUP BY forum) tf LEFT JOIN (SELECT COUNT(id) AS replies, MAX(time) AS lastreply, forum FROM message GROUP BY forum) mf ON tf.forum = mf.forum) tm ON f.id = tm.forum ORDER BY f.id ASC;
