Columbia is very lenient when it comes to drug and alcohol offenses, and disciplinary action usually does not extend past a Saturday class on drug safety. Rules do exist, and all freshman dorms are "dry" (no alcohol allowed) in theory, but enforcement of these rules is generally lax. Rule enforcement is generally up to dorm RAs, and most will let you get away with things as long as there are no complaints.
That being said, Public Safety has no qualms with breaking up a dorm party or taking down names of students who are belligerently drunk. Additionally, Columbia is very concerned about the safety of its students and will call CAVA (Columbia Area Volunteer Ambulance, a free student-run ambulance service) if a student is too drunk to walk straight/function properly. Safety comes first, and students are generally not reprimanded after being treated for overindulgence. Additionally, the NYPD is rarely if ever involved in student activities, with exceptions being made in particularly extreme or off-campus cases.