ASP statement judgment problem when SQL database is null

I have a table test1, there is a field num, the field num has a null value, there is a null value, and there are other values, and I want to use the ASP statement to determine whether the value of num I am querying is a null value. How to write

 

 be rigorous, with two layers of judgment: 
 
 If IsNull (rs ("num")) Or rs ("num") = "Then 
 ..... 
 End If 
 because the field is sometimes written to empty data, if it is written, but the data is empty, the value of the field is empty (""), and it is not NULL, so there are two layers to judge. 
 
 ... 

<td> Order Amount Statistics </td>
<td><%

sql= "select SUM (Price) as Num from [T_order] where DateDiff (' d ', Addtime,now ()) =0 "&wherestr&" "

Set Rs=server.createobject (" Adodb.recordset ")
Rs.Open sql,conn,0,1
' rs_total=rs (0)

If IsNull (rs ("num")) Or rs ("num") = "then
Response.Write" 0 "
Els E
Response.Write ("num")
End If

Rs.close
Set rs = Nothing
%>
</td>

SQL database n ULL the ASP statement to determine the problem