Count the number of captains that have each rank.
SELECT count(*) ,  rank FROM captain GROUP BY rank
SELECT count(*) ,  rank FROM captain GROUP BY rank
[{'count(*)': 1, 'Rank': 'Commander, junior captain'}, {'count(*)': 2, 'Rank': 'Lieutenant'}, {'count(*)': 4, 'Rank': 'Midshipman'}]