Implement GROUP BY clause functionality

library/Icinga/Data/Db/DbQuery.php

@@ -59,6 +59,13 @@ class DbQuery extends SimpleQuery
      */
     protected $count;
 
+    /**
+     * GROUP BY clauses
+     *
+     * @var string|array
+     */
+    protected $group;
+
     protected function init()
     {
         $this->db = $this->ds->getDbAdapter();
@@ -100,6 +107,10 @@ class DbQuery extends SimpleQuery
             }
         }
 
+        if ($this->group) {
+            $select->group($this->group);
+        }
+
         $select->columns($this->columns);
         $this->applyFilterSql($select);
 
@@ -300,4 +311,17 @@ class DbQuery extends SimpleQuery
     {
         return (string) $this->getSelectQuery();
     }
+
+    /**
+     * Add a GROUP BY clause
+     *
+     * @param   string|array $group
+     *
+     * @return  $this
+     */
+    public function group($group)
+    {
+        $this->group = $group;
+        return $this;
+    }
 }