CREATE TABLE Ship (Ship_ID INT, Name TEXT, Type TEXT, Built_Year FLOAT, Class TEXT, Flag TEXT)
CREATE TABLE captain (Captain_ID INT, Name TEXT, Ship_ID INT, age TEXT, Class TEXT, Rank TEXT)

Stacked bar of class and the number of class colored by Rank
SELECT Class, COUNT(Class) FROM captain GROUP BY Rank, Class
SELECT "Class", COUNT("Class") FROM "captain" GROUP BY "Rank", "Class"