SQLD 기출문제 예상문제 383번

다음 문제를 풀어보세요.

다음 SQL 쿼리의 실행 결과에 대한 설명으로 가장 적절한 것을 고르시오.

[테이블 구조]

CREATE TABLE EMPLOYEES (
    EMP_ID VARCHAR2(10) PRIMARY KEY,
    EMP_NAME VARCHAR2(50),
    DEPT_ID VARCHAR2(10),
    HIRE_DATE DATE,
    SALARY NUMBER
);

CREATE TABLE CONTRACTORS (
    CONT_ID VARCHAR2(10) PRIMARY KEY,
    CONT_NAME VARCHAR2(50),
    PROJECT_ID VARCHAR2(10),
    START_DATE DATE,
    CONTRACT_AMOUNT NUMBER
);

[샘플 데이터]

-- EMPLOYEES 테이블
| EMP_ID | EMP_NAME | DEPT_ID   | HIRE_DATE  | SALARY |
|--------|----------|-----------|------------|--------|
| E001   | 김철수   | SALES     | 2020-01-01 | 5000   |
| E002   | 이영희   | SALES     | 2021-03-15 | 5200   |
| E003   | 박민수   | DEV       | 2019-07-01 | 6000   |
| E004   | 김철수   | MARKETING | 2020-01-01 | 4800   |

-- CONTRACTORS 테이블
| CONT_ID | CONT_NAME | PROJECT_ID | START_DATE | CONTRACT_AMOUNT |
|---------|-----------|------------|------------|-----------------|
| C001    | 이철민    | PJT_SALES  | 2022-05-01 | 3000            |
| C002    | 김영수    | PJT_DEV    | 2023-01-10 | 3500            |
| C003    | 김철수    | PJT_SALES  | 2020-01-01 | 2800            |

[SQL 쿼리]

SELECT EMP_NAME AS PERSON_NAME, HIRE_DATE AS JOIN_START_DATE
FROM EMPLOYEES
WHERE DEPT_ID = 'SALES'
UNION ALL
SELECT CONT_NAME AS PERSON_NAME, START_DATE AS JOIN_START_DATE
FROM CONTRACTORS
WHERE PROJECT_ID = 'PJT_SALES';