select sum(金额) 金额, convert(char(6),时间 , 112) 年月 from TB
where datediff(mm,时间,getdate())<3 and  datediff(mm,时间,getdate())> 0
group by  convert(char(6),时间 , 112)

------解决方案--------------------

select sum(金额) 金额, userName, convert(char(6),时间 , 112) 年月 from TB
where datediff(mm,时间,getdate())<3 and  datediff(mm,时间,getdate())> 0
group by  convert(char(6),时间 , 112),userName

------解决方案--------------------

SQL code

--最猥琐的方法实现的，我也不知道你统计的时候按不按用户分组，嘿嘿！
create table test
(
    username varchar(20),
    sum decimal(18,5),
    CreateDate datetime
)

insert into test values
('a', 1 ,GETDATE()-30)
insert into test values
('b', 3 ,GETDATE()-30)
insert into test values
('c', 2 ,GETDATE()-30)
insert into test values
('d', 5 ,GETDATE()-30)




Create PROCEDURE testGetData
    -- Add the parameters for the stored procedure here
    
AS
BEGIN
    -- SET NOCOUNT ON added to prevent extra result sets from
    -- interfering with SELECT statements.
    SET NOCOUNT ON;

    -- Insert statements for procedure here
        
    declare @year char(4),@month char(2),@beginDate varchar(10),@endDate varchar(10)
    set @year=year(getdate())
    set @month=month(getdate())
    if(@month=1)
        begin
            set @beginDate=cast(@year-1 as varchar(4))+'11-01'
            set @endDate=cast(@year as varchar(4))+'01-01'
        end
    else if(@month=2)
        begin
            set @beginDate=cast(@year-1 as varchar(4))+'12-01'
            set @endDate=cast(@year as varchar(4))+'02-01'
        end
    else
         begin
            set @beginDate=cast((@year-1)as varchar(10))+'-'+cast((@month-2)as varchar(2))+'-01'
            set @endDate=cast(@year as varchar(10))+'-'+cast((@month)as varchar(2))+'-01'
         end
    
    print @beginDate
    print @endDate
    select username, SUM(sum) as totle from test
    where CreateDate >= CONVERT(VARCHAR(10),@beginDate,120) and CreateDate< CONVERT(VARCHAR(10),@endDate,120) 
    group by username


END
GO