fix issue #3704 regarding integer attribute values being cast to decimal

Author: Raphael Petrini

app/code/Magento/Eav/Model/Entity/Collection/AbstractCollection.php

@@ -1175,7 +1175,11 @@ public function _loadAttributes($printQuery = false, $logQuery = false)
         foreach ($selectGroups as $selects) {
             if (!empty($selects)) {
                 try {
-                    $select = implode(' UNION ALL ', $selects);
+                    if (is_array($selects))
+                    {
+                        $select = implode(' UNION ALL ', $selects);
+                    }
+                    else $select = $selects;
                     $values = $this->getConnection()->fetchAll($select);
                 } catch (\Exception $e) {
                     $this->printLogQuery(true, true, $select);

app/code/Magento/Eav/Model/ResourceModel/Helper.php

@@ -80,6 +80,6 @@ public function getLoadAttributesSelectGroups($selects)
         foreach ($selects as $selectGroup) {
             $mainGroup = array_merge($mainGroup, $selectGroup);
         }
-        return [$mainGroup];
+        return $mainGroup;
     }
 }