CREATE TABLE Has_Allergy (StuID INT, Allergy VARCHAR)
CREATE TABLE Allergy_Type (Allergy VARCHAR, AllergyType VARCHAR)
CREATE TABLE Student (StuID INT, LName VARCHAR, Fname VARCHAR, Age INT, Sex VARCHAR, Major INT, Advisor INT, city_code VARCHAR)

How many students live in each city, I want to show total number from high to low order.
SELECT city_code, COUNT(*) FROM Student GROUP BY city_code ORDER BY COUNT(*) DESC
SELECT "city_code", COUNT(*) FROM "Student" GROUP BY "city_code" ORDER BY COUNT(*) DESC NULLS LAST