It is true that sugar-free drinks do not have sugar in them. Previously, someone did an experiment in which two bottles of the same brand and the same flavor were boiled in a pot with sugar and sugar-free drinks, and the experiment found that a large amount of sugar was precipitated at the bottom of the pot with sugar, while no sugar was precipitated in the sugar-free drinks.
Sugar-free drinks are sweet because sugar substitutes are added to sugar-free drinks. Take aspartame as an example. As a substitute for sugar, aspartame is added to sugar-free drinks, and it has the same taste as sugary drinks in terms of taste.
But the same dose of aspartame is sweeter than sugar, so in sugar-free drinks, the amount of aspartame added is very small, even ignored in calories, which is also the reason why sugar-free drinks are 0 calories.