HostgroupsummaryQuery: Add empty groups to the union

refs #3928

modules/monitoring/library/Monitoring/Backend/Ido/Query/EmptyhostgroupQuery.php

@@ -0,0 +1,36 @@
+<?php
+/* Icinga Web 2 | (c) 2019 Icinga GmbH | GPLv2+ */
+
+namespace Icinga\Module\Monitoring\Backend\Ido\Query;
+
+class EmptyhostgroupQuery extends HostgroupQuery
+{
+    protected $subQueryTargets = [];
+
+    protected $columnMap = [
+        'hostgroups' => [
+            'hostgroup'             => 'hgo.name1 COLLATE latin1_general_ci',
+            'hostgroup_alias'       => 'hg.alias COLLATE latin1_general_ci',
+            'hostgroup_name'        => 'hgo.name1',
+            'host_name'             => '(NULL)',
+            'service_description'   => '(NULL)',
+            'servicegroup_name'     => '(NULL)'
+        ],
+        'instances' => [
+            'instance_name'         => 'i.instance_name'
+        ]
+    ];
+
+    protected function joinBaseTables()
+    {
+        parent::joinBaseTables();
+
+        $this->select->joinLeft(
+            ['ehgm' => $this->prefix . 'hostgroup_members'],
+            'ehgm.hostgroup_id = hg.hostgroup_id',
+            []
+        );
+        $this->select->group(['hgo.object_id', 'hg.hostgroup_id']);
+        $this->select->having('COUNT(ehgm.hostgroup_member_id) = ?', 0);
+    }
+}

modules/monitoring/library/Monitoring/Backend/Ido/Query/HostgroupsummaryQuery.php

@@ -108,7 +108,24 @@ class HostgroupsummaryQuery extends IdoQuery
             )
         );
         $this->subQueries[] = $services;
-        $this->summaryQuery = $this->db->select()->union(array($hosts, $services), Zend_Db_Select::SQL_UNION_ALL);
+        $emptyGroups = $this->createSubQuery(
+            'Emptyhostgroup',
+            [
+                'hostgroup_alias',
+                'hostgroup_name',
+                'host_handled'      => new Zend_Db_Expr('NULL'),
+                'host_severity'     => new Zend_Db_Expr('0'),
+                'host_state'        => new Zend_Db_Expr('NULL'),
+                'service_handled'   => new Zend_Db_Expr('NULL'),
+                'service_severity'  => new Zend_Db_Expr('0'),
+                'service_state'     => new Zend_Db_Expr('NULL'),
+            ]
+        );
+        $this->subQueries[] = $emptyGroups;
+        $this->summaryQuery = $this->db->select()->union(
+            [$hosts, $services, $emptyGroups],
+            Zend_Db_Select::SQL_UNION_ALL
+        );
         $this->select->from(array('hostgroupsummary' => $this->summaryQuery), array());
         $this->group(array('hostgroup_name', 'hostgroup_alias'));
         $this->joinedVirtualTables['hostgroupsummary'] = true;