[프로그래머스]중복 제거하기 (mysql)

문제

풀이 1

SELECT COUNT(DISTINCT NAME) AS 'count'
FROM ANIMAL_INS
WHERE NAME IS NOT NULL

풀이 2

select count(*) from (select distinct NAME from ANIMAL_INS) a
where name is not null

풀이 3

select count(a.name)
from (SELECT name
from ANIMAL_INS
group by name) a