SQL_LEVEL 1

1.이름이 없는 동물의 아이디

https://programmers.co.kr/learn/courses/30/lessons/59039

SELECT ANIMAL_ID
FROM ANIMAL_INS
WHERE NAME IS NULL

2.이름이 있는 동물의 아이디

https://programmers.co.kr/learn/courses/30/lessons/59407

SELECT ANIMAL_ID
FROM ANIMAL_INS
WHERE NAME IS NOT NULL
ORDER BY ANIMAL_ID

3.NULL처리하기

https://programmers.co.kr/learn/courses/30/lessons/59410

SELECT ANIMAL_TYPE, IFNULL(NAME,"No name") as NAME, SEX_UPON_INTAKE
FROM ANIMAL_INS