将上个月 A 列的值更新为当月 B 列 - Sql Server

Question

我有一张桌子“ABC”：

ID  CustomId      A              B              Month           Year
1      1         600             0                11            2016
2      1         500             0                12            2016
3      1         100             0                1             2017
4      1         200             0                2             2017
5      1         300             0                3             2017
6      2         300             0                1             2017
7      2         400             0                2             2017
8      2         500             0                3             2017

我想将上个月 A 列的值更新为当月的 B 列。

Answer 1

update tb set b = ta.a
  from abc ta
 inner join abc tb
         on DATEADD(m, cast(ta.year as varchar(10)) + '/'
                       + cast(ta.month as varchar(10)) + '/01'
                     , -1)
            = cast(tb.year as varchar(10)) + '/' + cast(tb.month as varchar(10)) + '/01'