[SQL문제풀기] 조건에 맞는 회원수 구하기

문제

MYSQL

내가 작성한 정답

SELECT COUNT(*) USERS
FROM USER_INFO
WHERE AGE BETWEEN 20 AND 29 
    AND DATE_FORMAT(JOINED,'%Y') = '2021';

SELECT COUNT(*) USERS
FROM (SELECT USER_ID
        FROM USER_INFO
        WHERE AGE BETWEEN 20 AND 29 
            AND DATE_FORMAT(JOINED,'%Y') = '2021') A;

ORACLE

내가 작성한 정답

SELECT COUNT(*) USERS
FROM USER_INFO
WHERE TO_CHAR(JOINED,'YYYY') = '2021'
    AND AGE BETWEEN 20 AND 29;

SELECT COUNT(*) USERS
FROM (SELECT USER_ID
      FROM USER_INFO
      WHERE TO_CHAR(JOINED,'YYYY') = '2021'
        AND AGE BETWEEN 20 AND 29);