存储过程取字段值遇到问题

[color2002]

create proc search_d_pro
@sid int,
@d varchar(50),
@year int,
@month int,
@ddd varchar(50) out
as
begin
--select @ddd=isnull(sum(cast(@d as float)),0) from pw_data
--where s_id=@sid and year(dateandtime)=@year and month(dateandtime)=@month and isnumeric(@d)=1
if(@d='d1')
select @ddd=isnull(sum(cast(d1 as float)),0) from pw_data
where s_id=@sid and year(dateandtime)=@year and month(dateandtime)=@month and isnumeric(d1)=1
else if(@d='d6')
select @ddd=isnull(sum(cast(d6 as float)),0) from pw_data
where s_id=@sid and year(dateandtime)=@year and month(dateandtime)=@month and isnumeric(d6)=1
else
select @ddd=isnull(sum(cast(d7 as float)),0) from pw_data
where s_id=@sid and year(dateandtime)=@year and month(dateandtime)=@month and isnumeric(d7)=1
end
go

请大家注意看一下注释掉的两行：
--select @ddd=isnull(sum(cast(@d as float)),0) from pw_data
--where s_id=@sid and year(dateandtime)=@year and month(dateandtime)=@month and isnumeric(@d)=1
如果这样写的话，@d传递过来的值为三个中的一个：d1,d6,d7,
取出来的值一直为null,
页通过下面判断@d的值，分别写SQL语句就能取出来，
if(@d='d1')
select @ddd=isnull(sum(cast(d1 as float)),0) from pw_data
where s_id=@sid and year(dateandtime)=@year and month(dateandtime)=@month and isnumeric(d1)=1
else if(@d='d6')
select @ddd=isnull(sum(cast(d6 as float)),0) from pw_data
where s_id=@sid and year(dateandtime)=@year and month(dateandtime)=@month and isnumeric(d6)=1
else
select @ddd=isnull(sum(cast(d7 as float)),0) from pw_data
where s_id=@sid and year(dateandtime)=@year and month(dateandtime)=@month and isnumeric(d7)=1
end
由此我判断是在select @ddd=isnull(sum(cast(@d as float)),0) from pw_data中，＠d没有取到值造成的，
其他的几个参数都可以传进来的，
各位老大知道是什么原因吗？

[doubon]

顶！

[color2002]

没人知道吗？

[Softlee81307]

select @ddd=isnull(sum(cast(@d as float)),0) from pw_data
這段要改成動態的
exec('select '+@ddd+'=isnull(sum(cast('+@d+' as float)),0) from pw_data')

[web_gus]

up

[Softlee81307]

exec(
'select '+@ddd+'=isnull(sum(cast('+@d+' as float)),0) from pw_data
where s_id='+cast(@sid as varchar(6))+' and year(dateandtime)='+cast(@year as varchar(4))+' and month(dateandtime)='+cast(@month as varchar(2)) )

[color2002]

照Softlee81307(孔腎)的方法，报如下错误：
服务器: 消息 170，级别 15，状态 1，行 1
第 1 行: '=' 附近有语法错误。

（所影响的行数为 1 行）

可能是exec(
'select '+@ddd+'=isnull(sum(cast('+@d+' as float)),0) from pw_data 这行中的＝号报错