What shall I order at the bar if I don't want alcohol--or sugar?

Something mildly sweet but sugar-free would be fine, and carbonated is fine too.

Usually in this sort of situation, a cocktail/social occasion, I have a glass of white wine. This time I’m attending an event where I don’t want to have anything with alcohol, and a traditional ginger ale won’t do because I have to avoid the sugar. It’s been so long since I’ve been in this situation that I can’t remember what I used to do.

These days I think there are probably a lot more choices, such as the fruit-flavored sparkling waters, but I never use them and would prefer not to look like a complete idiot when trying to order. I’ll resort to a diet Coke only if I have to.

Suggestions?

Tags as I wrote them: beverages, nonalcoholic cocktails, sparkling water, drinks.