In geographic identifier from 20 to 50, how many of them has a number of inhabitants below 20?
geographic identifier from 20 to 50 refers to GEOID BETWEEN 20 AND 50; number of inhabitants below 20 refers to INHABITANTS_K < 20;
SELECT COUNT(GEOID) FROM Demog WHERE INHABITANTS_K < 20 AND GEOID >= 20 AND GEOID <= 50