Merge pull request #324 from phpbb/fix/nonaggregated_columns_mysql

Add nonaggregated columns to group by clause

contribution/style/demo/demo.php

@@ -182,7 +182,7 @@ public function load_styles()
 								AND c.contrib_demo <> ""
 								AND rp.phpbb_version_branch = ' . (int) $this->phpbb_branch,
 
-			'GROUP_BY'	=> 'c.contrib_id',
+			'GROUP_BY'	=> 'c.contrib_id, cat.left_id, cat.category_name, s.attachment_id',
 			'ORDER_BY'	=> 'cat.left_id, c.contrib_name ASC',
 		);