SQLD 기출문제 예상문제 18번

다음 문제를 풀어보세요.

다음 중 성능 관점에서 가장 비효율적인 SQL 쿼리를 고르시오.

다음 ORDERS 테이블과 CUSTOMERS 테이블이 주어졌을 때, 주문 금액이 평균 주문 금액보다 큰 고객의 이름과 주문 금액을 조회하는 쿼리를 작성해야 합니다.
CREATE TABLE CUSTOMERS (
    CUSTOMER_ID INT PRIMARY KEY,
    CUSTOMER_NAME VARCHAR(255)
);

CREATE TABLE ORDERS (
    ORDER_ID INT PRIMARY KEY,
    CUSTOMER_ID INT,
    ORDER_AMOUNT DECIMAL(10, 2),
    FOREIGN KEY (CUSTOMER_ID) REFERENCES CUSTOMERS(CUSTOMER_ID)
);

SELECT C.CUSTOMER_NAME, O.ORDER_AMOUNT
FROM CUSTOMERS C
JOIN ORDERS O ON C.CUSTOMER_ID = O.CUSTOMER_ID
WHERE O.ORDER_AMOUNT > (SELECT AVG(ORDER_AMOUNT) FROM ORDERS);

SELECT C.CUSTOMER_NAME, O.ORDER_AMOUNT
FROM CUSTOMERS C
JOIN ORDERS O ON C.CUSTOMER_ID = O.CUSTOMER_ID
WHERE O.ORDER_AMOUNT > ALL (SELECT AVG(ORDER_AMOUNT) FROM ORDERS);

SELECT C.CUSTOMER_NAME, O.ORDER_AMOUNT
FROM CUSTOMERS C
JOIN ORDERS O ON C.CUSTOMER_ID = O.CUSTOMER_ID
WHERE O.ORDER_AMOUNT > (SELECT AVG(ORDER_AMOUNT) FROM (SELECT ORDER_AMOUNT FROM ORDERS) AS TEMP);

SELECT C.CUSTOMER_NAME, O.ORDER_AMOUNT
FROM CUSTOMERS C
JOIN ORDERS O ON C.CUSTOMER_ID = O.CUSTOMER_ID
WHERE O.ORDER_AMOUNT > (SELECT AVG(O2.ORDER_AMOUNT) FROM ORDERS O2);