It's common to hear "How should I address you?" This is equivalent to the people here suggesting a "nickname" field (good idea).
There are people with only one name. Don't make them double it (Ananda Ananda).
There are people with several given names. But they may only want to be called by the first, or the first two, or the last.
There are people who wish to be called by their full name. They may find it jarring to be addressed by just one piece of their name.
Finally there are people who go by a name which is not part of their legal name at all. Short forms like Bob instead of Robert, but also freeform names for various reasons, perhaps the most sensitive being that some government official may have determined their legal name contrary to their own wishes. Imagine your mother named you Sue but someone decided that must be short for Susan and put that on your government documents.
Related: when people want to show which part of their name is the family name, they either make it all uppercase or underline it. You can see this on some CVs but it happens elsewhere too when a full name is going to be read by people who don't know the addressee.