SQL doesn't have a data format for subnets, so solarwinds is storing them as a string and you are trying to greater than against a string, which tends to be a complete mess. I expect the way I would get this to work would be a fully custom SQL alert condition that breaks the last octet off with a substring, converts it to an integer, then does the greater than compare.
Not easy to do at all on a Friday afternoon.
If you really want to stick to it I guess you could also try and do something like starts with "192.168.1.2" and does not end with 1.2 and does not end with 1.21,.22, .23, etc etc It's caveman style but would work if you aren't actually a DBA on the side.
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