递归相减如何处理?

Question

t1:                                                 
dt decimal(8,0),                                    
amt decimal(15,2),                                  
amt1 decimal(15,2)                                  
                                                    
原数据:                                             
200601   1  0                                       
200602   2  0                                       
200603   3  0                                       
200604   4  0                                       
200605   5  0                                       
200606   6  0                                       
200607   7  0                                       
200608   8  0                                       
200609   9  0                                       
200610   10 0                                       
200611   11 0                                       
200612   12 0                                       
200701   2  0                                       
200702   5  0                                       
希望结果:                                           
200601   1  1                                       
200602   2  1                                       
200603   3  1                                       
200604   4  1                                       
200605   5  1                                       
200606   6  1                                       
200607   7  1                                       
200608   8  1                                       
200609   9  1                                       
200610   10 1                                       
200611   11 1                                       
200612   12 1                                       
200701   2  2                                       
200702   5  3                                       
一月份AMT放入AMT1,其他是后月AMT减上月AMT放入AMT1    

Answer 1

declare @t table(dt int,amt int,amt1 int)
insert into @t select 200601, 1,0
insert into @t select 200602, 2,0
insert into @t select 200603, 3,0
insert into @t select 200604, 4,0
insert into @t select 200605, 5,0
insert into @t select 200606, 6,0
insert into @t select 200607, 7,0
insert into @t select 200608, 8,0
insert into @t select 200609, 9,0
insert into @t select 200610,10,0
insert into @t select 200611,11,0
insert into @t select 200612,12,0
insert into @t select 200701, 2,0
insert into @t select 200702, 5,0select  
    dt,amt,amt-isnull((select amt from @t where dt=t.dt-1),0) as amt1
from 
    @t t

Answer 2

declare @t table(dt int,amt int,amt1 int)
insert into @t select 200601, 1,0
insert into @t select 200602, 2,0
insert into @t select 200603, 3,0
insert into @t select 200604, 4,0
insert into @t select 200605, 5,0
insert into @t select 200606, 6,0
insert into @t select 200607, 7,0
insert into @t select 200608, 8,0
insert into @t select 200609, 9,0
insert into @t select 200610,10,0
insert into @t select 200611,11,0
insert into @t select 200612,12,0
insert into @t select 200701, 2,0
insert into @t select 200702, 5,0select  
    dt,amt,amt-isnull((select amt from @t where dt=t.dt-1),0) as amt1
from 
    @t t/*
dt          amt         amt1        
----------- ----------- ----------- 
200601      1           1
200602      2           1
200603      3           1
200604      4           1
200605      5           1
200606      6           1
200607      7           1
200608      8           1
200609      9           1
200610      10          1
200611      11          1
200612      12          1
200701      2           2
200702      5           3
*/update t
set 
    amt1=amt-isnull((select amt from @t where dt=t.dt-1),0)
from 
    @t tselect * from @t/*
dt          amt         amt1        
----------- ----------- ----------- 
200601      1           1
200602      2           1
200603      3           1
200604      4           1
200605      5           1
200606      6           1
200607      7           1
200608      8           1
200609      9           1
200610      10          1
200611      11          1
200612      12          1
200701      2           2
200702      5           3
*/