IS NULL

-- MySQL
SELECT ANIMAL_ID
FROM ANIMAL_INS
WHERE NAME IS NULL
ORDER BY ANIMAL_ID

경기도에 위치한 식품창고 목록 출력하기

FOOD_WAREHOUSE 테이블에서 경기도에 위치한 창고의 ID, 이름, 주소, 냉동시설 여부를 조회하는 SQL문을 작성해주세요. 이때 냉동시설 여부가 NULL인 경우, 'N'으로 출력시켜 주시고 결과는 창고 ID를 기준으로 오름차순 정렬해주세요.

COALESCE

-- 공통
SELECT WAREHOUSE_ID, WAREHOUSE_NAME, ADDRESS, COALESCE(FREEZER_YN, 'N') AS FREEZER_YN
FROM FOOD_WAREHOUSE
WHERE WAREHOUSE_NAME LIKE '%경기%'
ORDER BY WAREHOUSE_ID

NVL

-- Oracle
SELECT WAREHOUSE_ID, WAREHOUSE_NAME, ADDRESS, NVL(FREEZER_YN, 'N') AS FREEZER_YN
FROM FOOD_WAREHOUSE
WHERE WAREHOUSE_NAME LIKE '%경기%'
ORDER BY WAREHOUSE_ID

IFNULL

-- MySQL
SELECT WAREHOUSE_ID, WAREHOUSE_NAME, ADDRESS, IFNULL(FREEZER_YN, 'N') AS FREEZER_YN
FROM FOOD_WAREHOUSE
WHERE WAREHOUSE_NAME LIKE '%경기%'
ORDER BY WAREHOUSE_ID

---

이름이 없는 동물의 아이디

동물 보호소에 들어온 동물 중, 이름이 없는 채로 들어온 동물의 ID를 조회하는 SQL 문을 작성해주세요. 단, ID는 오름차순 정렬되어야 합니다.

SELECT ANIMAL_ID
FROM ANIMAL_INS
WHERE NAME IS NULL
ORDER BY ANIMAL_ID

---

이름이 있는 동물의 아이디

동물 보호소에 들어온 동물 중, 이름이 있는 동물의 ID를 조회하는 SQL 문을 작성해주세요. 단, ID는 오름차순 정렬되어야 합니다.

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

---

NULL 처리하기

입양 게시판에 동물 정보를 게시하려 합니다. 동물의 생물 종, 이름, 성별 및 중성화 여부를 아이디 순으로 조회하는 SQL문을 작성해주세요. 이때 프로그래밍을 모르는 사람들은 NULL이라는 기호를 모르기 때문에, 이름이 없는 동물의 이름은 "No name"으로 표시해 주세요.

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

---

나이 정보가 없는 회원 수 구하기

USER_INFO 테이블에서 나이 정보가 없는 회원이 몇 명인지 출력하는 SQL문을 작성해주세요. 이때 컬럼명은 USERS로 지정해주세요.

SELECT COUNT(*) AS USERS
FROM USER_INFO
WHERE AGE IS NULL

---

ROOT 아이템 구하기

ROOT 아이템을 찾아 아이템 ID(ITEM_ID), 아이템 명(ITEM_NAME)을 출력하는 SQL문을 작성해 주세요. 이때, 결과는 아이템 ID를 기준으로 오름차순 정렬해 주세요.

SELECT I.ITEM_ID, I.ITEM_NAME
FROM ITEM_INFO I
LEFT JOIN ITEM_TREE T
    ON I.ITEM_ID = T.ITEM_ID
WHERE T.PARENT_ITEM_ID IS NULL
ORDER BY I.ITEM_ID

---

업그레이드 할 수 없는 아이템 구하기

더 이상 업그레이드할 수 없는 아이템의 아이템 ID(ITEM_ID), 아이템 명(ITEM_NAME), 아이템의 희귀도(RARITY)를 출력하는 SQL 문을 작성해 주세요. 이때 결과는 아이템 ID를 기준으로 내림차순 정렬해 주세요.

SELECT ITEM_ID, ITEM_NAME, RARITY
FROM ITEM_INFO I
WHERE NOT EXISTS (
    SELECT 1
    FROM ITEM_TREE T
    WHERE T.PARENT_ITEM_ID = I.ITEM_ID
    GROUP BY T.PARENT_ITEM_ID
)
ORDER BY ITEM_ID DESC

---

잡은 물고기의 평균 길이 구하기

잡은 물고기의 평균 길이를 출력하는 SQL문을 작성해주세요.
평균 길이를 나타내는 컬럼 명은 AVERAGE_LENGTH로 해주세요.
평균 길이는 소수점 3째자리에서 반올림하며, 10cm 이하의 물고기들은 10cm 로 취급하여 평균 길이를 구해주세요.

SELECT ROUND(AVG(COALESCE(LENGTH, 10)), 2) AS AVERAGE_LENGTH
FROM FISH_INFO