Merge pull request #2257 from kurund/CRM-14004

fixes for CRM-14004, duplicate memberships

CRM/Export/BAO/Export.php

@@ -554,6 +554,20 @@ INSERT INTO {$componentTable} SELECT distinct gc.contact_id FROM civicrm_group_c
       $groupBy = " GROUP BY contact_a.id";
     }
 
+    switch ($exportMode) {
+      case CRM_Export_Form_Select::CONTRIBUTE_EXPORT:
+        $groupBy = 'GROUP BY civicrm_contribution.id';
+        break;
+
+      case CRM_Export_Form_Select::EVENT_EXPORT:
+        $groupBy = 'GROUP BY civicrm_participant.id';
+        break;
+
+      case CRM_Export_Form_Select::MEMBER_EXPORT:
+        $groupBy = " GROUP BY civicrm_membership.id";
+        break;
+    }
+
     if ($queryMode & CRM_Contact_BAO_Query::MODE_ACTIVITY) {
       $groupBy = " GROUP BY civicrm_activity.id ";
     }