how to difference whether the wine?

[Kcwhippet]

Whoever told you that is wrong. Generally speaking, the more mature the grapes at harvest, the more sugars they have, which translates into higher alcohol. The sugar is converted into alcohol by the yeast during fermentation, so if there's more sugar the wine ends up with more alcohol if the winemaker ferments to dry, as they do with almost all wines. About the only exception is when the winemaker stops fermentation to leave some sugar to create a dessert wine. So whoever told you more alcohol means a sweet wine is very wrong.