A private key is an integer and your constant is also an integer so you can perform a simple comparison to see which one is bigger. But if by "the key" you mean the "public key" then it is impossible because as it was mentioned the whole underlying cryptography would have been deemed broken and people would have been able to start solving the ECDLP!
Fair enough You have a good point. A private key is just a gigantic number so comparing it to another number is kinda straightforward. But a public key isn't a number it's more like a point on a specific mathematical curve. Think of it like comparing a number to a physical street address they are fundamentally different kinds of data.
it's easy to get from your private key (the number) to your public key (the point on the curve), but it's computationally impossible to go back. If you could somehow compare a public key to an integer in a way that gave you a clue about the original private key you basically would have just turned that one way street into a two way street and the whole system would crumble.