--下面是例子
declare @t table(a nvarchar(10))
insert into @t
select '12'
union all select '234'
union all select '24'
union all select '34'
union all select '27'
union all select '2a' --这个是不能转换成数字的
select sum(case when isnumeric(a)=1 then cast(a as decimal(38,2)) else 0 end) from @t