SQLD 기출문제 예상문제 78번

다음 문제를 풀어보세요.

다음 중 부서별 급여 상위 3명의 사원을 추출하는 SQL 쿼리 중 성능상 가장 효율적인 것을 고르시오.

-- EMP 테이블 구조
CREATE TABLE EMP (
    EMPNO NUMBER(4) PRIMARY KEY,
    ENAME VARCHAR2(10),
    JOB VARCHAR2(9),
    MGR NUMBER(4),
    HIREDATE DATE,
    SAL NUMBER(7,2),
    COMM NUMBER(7,2),
    DEPTNO NUMBER(2)
);

-- 데이터 샘플
INSERT INTO EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) VALUES (7369, 'SMITH', 'CLERK', 7902, TO_DATE('17-DEC-80', 'DD-MON-RR'), 800, NULL, 20);
INSERT INTO EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) VALUES (7499, 'ALLEN', 'SALESMAN', 7698, TO_DATE('20-FEB-81', 'DD-MON-RR'), 1600, 300, 30);
INSERT INTO EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) VALUES (7521, 'WARD', 'SALESMAN', 7698, TO_DATE('22-FEB-81', 'DD-MON-RR'), 1250, 500, 30);
INSERT INTO EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) VALUES (7566, 'JONES', 'MANAGER', 7839, TO_DATE('02-APR-81', 'DD-MON-RR'), 2975, NULL, 20);
INSERT INTO EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) VALUES (7654, 'MARTIN', 'SALESMAN', 7698, TO_DATE('28-SEP-81', 'DD-MON-RR'), 1250, 1400, 30);
INSERT INTO EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) VALUES (7698, 'BLAKE', 'MANAGER', 7839, TO_DATE('01-MAY-81', 'DD-MON-RR'), 2850, NULL, 30);
INSERT INTO EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) VALUES (7782, 'CLARK', 'MANAGER', 7839, TO_DATE('09-JUN-81', 'DD-MON-RR'), 2450, NULL, 10);
INSERT INTO EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) VALUES (7788, 'SCOTT', 'ANALYST', 7566, TO_DATE('19-APR-87', 'DD-MON-RR'), 3000, NULL, 20);
INSERT INTO EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) VALUES (7839, 'KING', 'PRESIDENT', NULL, TO_DATE('17-NOV-81', 'DD-MON-RR'), 5000, NULL, 10);
INSERT INTO EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) VALUES (7844, 'TURNER', 'SALESMAN', 7698, TO_DATE('08-SEP-81', 'DD-MON-RR'), 1500, 0, 30);
INSERT INTO EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) VALUES (7876, 'ADAMS', 'CLERK', 7788, TO_DATE('23-MAY-87', 'DD-MON-RR'), 1100, NULL, 20);
INSERT INTO EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) VALUES (7900, 'JAMES', 'CLERK', 7698, TO_DATE('03-DEC-81', 'DD-MON-RR'), 950, NULL, 30);
INSERT INTO EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) VALUES (7902, 'FORD', 'ANALYST', 7566, TO_DATE('03-DEC-81', 'DD-MON-RR'), 3000, NULL, 20);
INSERT INTO EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO) VALUES (7934, 'MILLER', 'CLERK', 7782, TO_DATE('23-JAN-82', 'DD-MON-RR'), 1300, NULL, 10);