Access - Update fields between a range of other fields - ms-access

Question

I have a list of IP Addresses in a table. I recently decided to identify these IP addresses by their division (I can't come up with a better name right now--their organization unit? Anyway, neither here nor there).
What I want to do is update the division for a range of IP Addresses. For example, I want to update the IP range of 192.168.1.10-192.168.1.50 to have a division of Local. I know it's something like this, I just can't figure it out:
UPDATE [IP Address Range]
SET [IP Address Range].Division = Local
WHERE [IP Address Range].[IP Addresses] >192.168.1.10 <192.168.1.50
Am I on the right track?

Answer 1

Since the IP addresses are represented using strings, any comparison would be performed on the ASCII character codes comprising the strings, which would return undesired results unless all sections of the IP address were to be padded to three characters with leading zeros (e.g. "192.168.001.050").
With padding, the string comparison would work because the characters would be compared with a character in the same position in each string, and by virtue of the fact that ASCII character codes for numerical characters are sequential and increasing with the numerical values.
Intepreting the strings as a numerical range in the format that they currently appear (i.e. without padding zeros) would require writing a function to parse each section of the period-delimited string, and comparing the numerical value of each section.
One way to achieve this is to convert the 4 bytes represented by the IPv4 address into a 32-bit integer (which will unfortunately need to be represented using a Double since VBA does not support 32-bit unsigned Integers), and then simply comparing the two numerical values using standard relational operators.
Here is a quick example:
Function IPValue(IPAddr As String) As Double
Dim byt
Dim fac As Long: fac = 16777216
For Each byt In Split(IPAddr, ".")
IPValue = IPValue + fac * byt
fac = fac / 256
Next byt
End Function
(unfortunately VBA also does not have a bitwise shift operator, otherwise this would be even shorter)
The range 192.168.1.10 to 192.168.1.50 then becomes:
?IPValue("192.168.1.10")
3232235786
?IPValue("192.168.1.50")
3232235826
Which, after defining the function in a public module, you can use in your SQL statement in the following manner:
UPDATE [IP Address Range] SET [IP Address Range].Division = "Local"
WHERE
IPValue([IP Address Range].[IP Addresses])
BETWEEN IPValue("192.168.1.10") AND IPValue("192.168.1.50")