IS NULL

https://programmers.co.kr/learn/courses/30/parts/17045

이름이 없는 동물의 아이디

SELECT ANIMAL_ID
FROM ANIMAL_INS
WHERE NAME IS NULL
ORDER BY ANIMAL_ID

이름이 있는 동물의 아이디

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

NULL 처리하기

SELECT ANIMAL_TYPE,IFNULL(NAME, 'No name'), SEX_UPON_INTAKE
FROM ANIMAL_INS
ORDER BY ANIMAL_ID

SELECT ANIMAL_TYPE,
    CASE WHEN NAME IS NULL THEN 'No name' else NAME END NAME,
    SEX_UPON_INTAKE
FROM ANIMAL_INS ORDER
BY ANIMAL_ID