You have to loop through them to find out which ones are/aren't blank -
Think of this:
'make a sql variable
dim sql
'start it with default value
sql = "UPDATE tableName set "
'check form vars and build statement accordingly
if request.form("val1"

<> "" then
sql = sql & "col1 = '" & request.form("val1"

& "',"
else
sql = sql & "col1 = NULL,"
end if
if request.form("val2"

<> "" then
sql = sql & "col2 = '" & request.form("val2"

& "',"
else
sql = sql & "col2 = NULL,"
end if
'chop off that last comma
sql = left(sql, len(sql)-1)
'add your where clause
sql = sql & " WHERE pkColumn = " & pkValue
'execute the statement
conObject.execute sql
Although simplified, this method works well for updating tables based on form inputs from users.

paul