아래 SQL 결과의 SELECT 컬럼 개수로 옳은 것은?
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[EMP]
| EMPNO | ENAME | HIREDATE | SAL |
|---|---|---|---|
| 7839 | KING | 1981-11-17 | 5000 |
| 7566 | JONES | 1981-04-02 | 2975 |
[EMP_HIST] (퇴사 이력)
| EMPNO | ENAME | HIREDATE | SAL |
|---|---|---|---|
| 7369 | SMITH | 1980-12-17 | 800 |
SELECT EMPNO, ENAME, EXTRACT(YEAR FROM HIREDATE) AS YR, SAL FROM EMP UNION SELECT EMPNO, ENAME, EXTRACT(YEAR FROM HIREDATE), SAL FROM EMP_HIST;
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