Insert NULL value into SQL Server from Classic ASP - sql-server

Question

I am trying to do a simple insert or update into SQL Server as NULL, not blank. I have seen many references online to just set Field = NULL without quotes but it is still coming up as empty, not NULL. Incredibly frustrating.
This is in classic asp.
If Request.Form("Field") = "" or IsNull(Request.Form("Field")) then
Field = NULL
Else
Field = Request.Form("Field")
End If
sSql="UPDATE [table] SET timestamp = {fn NOW()}," &_
"Field = '" & Field & "'," &_
"WHERE [System] = '" & System & "' and Active = '1'"
If I do this, it proves that it is checking because it puts in a 1.
If Request.Form("Field") = "" or IsNull(Request.Form("Field")) then
Field = 1
Else
Field = Request.Form("Field")
End If
sSql="UPDATE [table] SET timestamp = {fn NOW()}," &_
"Field = '" & Field & "'," &_
"WHERE [System] = '" & System & "' and Active = '1'"
I tried this but get an error 500:
sSql="UPDATE [Table] SET timestamp = {fn NOW()}, Field = "
If IsNull(Field) Then
sSQL = sSQL & "NULL"
Else
sSQL = sSQL & "'" & Field & "'" &_
End If
"NTLogon = '" & UCase(NTLogon) & "'" &_
"WHERE [System] = '" & System & "' and Active = '1'"
When I try this in place of my original code:
Field Assignment:
Field = "NULL" and Field = "'" & Request.Form("Field") & "'"
sSQL:
"Field = " & Field & "," &_
I get "An error occurred on the server when processing the URL."

Answer 1

So yeah, insert rant here about using parameterized queries, blah blah blah... now that's out of everyone's system, could we maybe look at the actual question?
The problem is this:
"Field = '" & Field & "'"
Those ampersands are converting your lovingly-populated vbScript NULL value right back into a string. If you don't want that to happen, you need to explicitly handle the IsNull case.
sSQL = "UPDATE [table] SET timestamp = {fn NOW()}, Field = "
If IsNull(Field) Then
sSQL = sSQL & "NULL"
Else
sSQL = sSQL & "'" & Field & "'"
End If
sSQL = sSQL & " WHERE [System] = '" & System & "' AND Active = '1'"
Note that even if you do this via a parameterized query, you'll need to make sure you're not appending your vbScript NULL value onto a string, because "" & NULL = "".

Answer 2

#pinchetpooche Hello there. I had the same issue and tried the given answer, and also received a 500 error page. I found that #Martha forgot to include the necessary SQL field that is being updated (i.e., "Field"). So I put together some test code, using her solution (i.e., using string concatenation and conditional logic), and executed against an actual database, and this solution works perfectly:
sSQLNullTest = "UPDATE CustomersToCCData SET "
sSQLNullTest = sSQLNullTest & "CustomerID = " & iCustomerID & ", "
If IsNull(x_license_number_state) Or x_license_number_state = "" Then
sSQLNullTest = sSQLNullTest & "CCLicenseState = NULL"
Else
sSQLNullTest = sSQLNullTest & "CCLicenseState = '" & x_license_number_state & "' "
End If
sSQLNullTest = sSQLNullTest & " WHERE CCID = '" & iCCInfoCCID & "'