I have uncovered a number of postgres sql specific errors which prevent a number of forum functions to work as designed.

/mod/hsfourum/renderer.php

Line apprx 307

Fails:
$replyusers = $DB->get_records_sql("SELECT DISTINCT $fields FROM

{hsuforum_posts} hp JOIN {user} u ON hp.userid = u.id WHERE hp.discussion = ? AND hp.privatereply = 0 ORDER BY hp.modified DESC", array($discussion->id));

Postgres requires the order by column to be part of the fields in the select

Works:

$replyusers = $DB->get_records_sql("SELECT DISTINCT $fields, hp.modified FROM{hsuforum_posts}

hp JOIN

{user}

u ON hp.userid = u.id WHERE hp.discussion = ? AND hp.privatereply = 0 ORDER BY hp.modified DESC", array($discussion->id));

Also,
lib/table/posters.php

Apprx Line 54 sql begins, must add u.id to group by apprx line 61 in order for sql to run in postgres.
Similar error group by clause.