Fix creation performance of form element menuparent, (slow down in me…

…nu item edit form, for item that belongs to large menu) (joomla#11628)

* Remove unused left join in getOptions for menuparent form element

* Replaced unneeded group by with distinct

* fix joomla#11628 for postgresql (#2)

in postgresql don't work as it is now , it give an **SQL ERROR**
 for the `ORDER BY` clause field used `a.lft` must be in the select list of fields when the `SELECT` use `DISTINCT()`

administrator/components/com_menus/models/fields/menuparent.php

@@ -39,9 +39,8 @@ protected function getOptions()
 
 		$db = JFactory::getDbo();
 		$query = $db->getQuery(true)
-			->select('a.id AS value, a.title AS text, a.level')
-			->from('#__menu AS a')
-			->join('LEFT', $db->quoteName('#__menu') . ' AS b ON a.lft > b.lft AND a.rgt < b.rgt');
+			->select('DISTINCT(a.id) AS value, a.title AS text, a.level, a.lft')
+			->from('#__menu AS a');
 
 		// Filter by menu type.
 		if ($menuType = $this->form->getValue('menutype'))
@@ -69,7 +68,6 @@ protected function getOptions()
 		}
 
 		$query->where('a.published != -2')
-			->group('a.id, a.title, a.level, a.lft, a.rgt, a.menutype, a.parent_id, a.published')
 			->order('a.lft ASC');
 
 		// Get the options.