LEFT JOIN hosts in the history view

Otherwise, MySQL won't utilize the event_time index.

Co-authored-by: Eric Lippmann <eric.lippmann@icinga.com>

Author: yhabteab

application/controllers/HistoryController.php

@@ -78,9 +78,11 @@ public function indexAction()
 
         $history->filter(Filter::lessThanOrEqual('event_time', $before));
         $this->filter($history, $filter);
+
+        $history->getWith()['history.host']->setJoinType('LEFT');
         $history->getSelectBase()
-            // Make sure we'll fetch service history entries only for services which still exist
-            ->where(['history.service_id IS NULL', 'history_service.id IS NOT NULL'], Sql::ANY);
+            // Because of LEFT JOINs, make sure we'll fetch history entries only for items which still exist:
+            ->where(['history_host.id IS NOT NULL', 'history_service.id IS NOT NULL'], Sql::ANY);
 
         yield $this->export($history);