PostgreSQL version: 9.3
A database error is thrown when visiting the Special:ActiveUsers page. Initially I ran into the issue described in bug 67594 but hand-patched DatabasePostgres.php (per the bug) to work around it. But even after that is fixed, a different error appears:
Query: SELECT user_name,user_id,COUNT(*) AS recentedits,qcc_title FROM "querycachetwo","mwuser","recentchanges" WHERE qcc_type = 'activeusers' AND qcc_namespace = '2' AND (user_name = qcc_title) AND (rc_user_text = qcc_title) AND (rc_type != '5') AND (NOT EXISTS (SELECT 1 FROM "ipblocks" WHERE (ipb_user=user_id) AND ipb_deleted = '1' )) GROUP BY qcc_title ORDER BY qcc_title LIMIT 51 Function: IndexPager::buildQueryInfo (ActiveUsersPager) Error: 42803 ERROR: column "mwuser.user_name" must appear in the GROUP BY clause or be used in an aggregate function LINE 1: ...ildQueryInfo (ActiveUsersPager) 188.8.131.52 */ user_name,... ^
Bug 21196 contains a similar error but in a completely different part of the code.
After some research, I understand the issue somewhat but the fix is currently beyond my own abilities.