create table test(YYYYMM char(7),AMT int,DIFF int)

insert test

(YYYYMM,AMT)

select '2008-01',594080 union all

select '2008-02',735061 union all

select '2008-03',1392355 union all

select '2008-04',1338021 union all

select '2008-05',1264786 union all

select '2008-06',1174275

-------------------------------------------------------

select a.YYYYMM,a.AMT,ISNULL(b.AMT,0)-a.AMT DIFF

 from test a left outer join test b

   on a.YYYYMM = convert(char(7),dateadd(mm,1,b.YYYYMM+'-01'),120)

/*

YYYYMM  AMT         DIFF

------- ----------- -----------

2008-01 594080      -594080

2008-02 735061      -140981

2008-03 1392355     -657294

2008-04 1338021     54334

2008-05 1264786     73235

2008-06 1174275     90511

(6개 행 적용됨)

*/