>DROP table #TT >create table #TT (AA INT PRIMARY KEY, BB INT) >CREATE INDEX IK ON #TT (BB) > >INSERT #TT SELECT 2*ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) > , 3*ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) > FROM sys.objects A,sys.objects B > >SELECT * FROM #TT WHERE AA = 4 OR BB = 3000 > >SELECT * FROM #TT WHERE AA = 4 > UNION > SELECT * FROM #TT WHERE BB = 3000 > >SELECT * FROM #TT WHERE AA = 4 OR BB = 6 > >SELECT * FROM #TT WHERE AA = 4 > UNION > SELECT * FROM #TT WHERE BB = 6 >I tried all that. It is interesting to see the adjustment in the execution when using UNION.