求教一个sql语句或存储过程

[zhizhubao]

在查询的时候，根据IsUpMessage,当前日期和DateUpExpired 通过特殊算法返回新的一列DateUpNew，
特殊算法如下：
If IsUpMessage Then
If NOW > DateUpExpired Then
Return DateUpExpired
Else
Return NULL
End If
Else
Return NULL
End If

不知道用sql语句能不能实现
希望各位大虾指点

[浩方软件HFWMS]

create proc p_is
@DateUpExpired datetime
@IsUpMessage varchar(10)
as
if @IsUpMessage<>''
begin
if getdate()> @DateUpExpired
select @DateUpExpired as DateUpExpired
return
else
select 'NULL'
else
select 'NULL'
end
go

[浩方软件HFWMS]

create proc p_is
@DateUpExpired datetime
@IsUpMessage varchar(10)
as
if @IsUpMessage<>''
begin
if getdate()> @DateUpExpired
select @DateUpExpired as DateUpExpired
return
else
select 'NULL'
return
else
select 'NULL'
return
end
go

[yjsmask]

SELECT CASE IsUpMessage WHEN TRUE THEN (CASE NOW() WHEN NOW()>DateUpExpired THEN DateUpExpired ELSE null END) ELSE NULL END from table

[paoluo]

Declare @DateUpExpired DateTime
Declare @DateUpNew DateTime
Declare @IsUpMessage Bit
--Set @DateUpExpired='2005-12-01'
Set @DateUpExpired='2005-12-02'
Set @IsUpMessage=1
Select @DateUpNew=(Case When @IsUpMessage=1 And DateDiff(dd,GetDate(),@DateUpExpired)<0 Then @DateUpExpired Else Null End)
Select @DateUpNew