Legal Question in Criminal Law in California

There's a huge difference. Drinking in public (also known as possession of alcohol in public) is usually a violation of a city or county ordinance, assuming you're over 18. It can be a misdemeanor or an infraction. Drunk in public is a misdemeanor violation of Penal Code section 647(f).

To prove drinking in public, they just have to show you possessed alcohol in an area that it was prohibited. To prove drunk in public [public intoxication under 647(f)], they have to show you were so intoxicated that you were unable to care for your own safety or the safety of others.

Sure. You can drink in public without becoming drunk. You can also be drunk in public after drinking in private. Neither of these charges implies that the defendant also committed the other.