diff --git a/lib/core/agent.py b/lib/core/agent.py
index 56ec22590..54fe28abe 100644
--- a/lib/core/agent.py
+++ b/lib/core/agent.py
@@ -833,10 +833,10 @@ class Agent(object):
                     if " WHERE " in limitedQuery:
                         limitedQuery = "%s AND %s " % (limitedQuery, self.nullAndCastField(uniqueField or field))
                     else:
-                        limitedQuery = "%s WHERE ISNULL(%s,' ') " % (limitedQuery, uniqueField or field)
+                        limitedQuery = "%s WHERE %s " % (limitedQuery, self.nullAndCastField(uniqueField or field))
 
                     limitedQuery += "NOT IN (%s" % (limitStr % num)
-                    limitedQuery += "%s %s ORDER BY %s) ORDER BY %s" % (self.nullAndCastField(uniqueField or field), fromFrom, uniqueField or "1", uniqueField or "1")
+                    limitedQuery += "%s %s ORDER BY %s) ORDER BY %s" % (self.nullAndCastField(uniqueField or field), fromFrom, uniqueField or field, uniqueField or field)
                 else:
                     if " WHERE " in limitedQuery:
                         limitedQuery = "%s AND %s " % (limitedQuery, field)
diff --git a/lib/techniques/union/use.py b/lib/techniques/union/use.py
index 1706b291c..b27b65cdb 100644
--- a/lib/techniques/union/use.py
+++ b/lib/techniques/union/use.py
@@ -28,6 +28,7 @@ from lib.core.common import isNoneValue
 from lib.core.common import isNumPosStrValue
 from lib.core.common import listToStrValue
 from lib.core.common import parseUnionPage
+from lib.core.common import prioritySortColumns
 from lib.core.common import removeReflectiveValues
 from lib.core.common import singleTimeDebugMessage
 from lib.core.common import singleTimeWarnMessage
@@ -244,7 +245,7 @@ def unionUse(expression, unpack=True, dump=False):
                                 break
 
                         if Backend.getIdentifiedDbms() in (DBMS.MSSQL, DBMS.SYBASE):
-                            field = expressionFieldsList[0]
+                            field = prioritySortColumns(expressionFieldsList)[0]
                         elif Backend.isDbms(DBMS.ORACLE):
                             field = expressionFieldsList
                         else: