SELECT d.deptno , d.dname , e.empno , e.ename FROM dept d INNER JOIN (SELECT deptno , empno , ename , ROW_NUMBER() OVER(PARTITION BY deptno ORDER BY empno) rn FROM emp ) e ON d.deptno = e.deptno WHERE e.rn = 1 ;
SELECT * FROM (SELECT d.deptno , d.dname , e.empno , e.ename , ROW_NUMBER() OVER(PARTITION BY d.deptno ORDER BY e.empno) rn FROM dept d INNER JOIN emp e ON d.deptno = e.deptno ) WHERE rn = 1 ;