Two issues in libraries/legacy/categories/categories.php cause query errors in Postgresql :

On line 222, the query should be :

$case_when .= $query->charLength('c.alias', '!=', '0');

on line 277+ "c.version" should be added to the group statement, eg:

$query->group('c.id, c.asset_id, c.access, c.alias, c.checked_out, c.checked_out_time,
c.created_time, c.created_user_id, c.description, c.extension, c.hits, c.language, c.level,
c.lft, c.metadata, c.metadesc, c.metakey, c.modified_time, c.note, c.params, c.parent_id,
c.path, c.published, c.rgt, c.title, c.modified_user_id, c.version');