SELECT LEVELS , 
	   (CASE WHEN LEVELS = 'H' THEN DEPTNO ELSE NULL END) DEPTNO, 
	   (CASE WHEN LEVELS = 'H' THEN DNAME ELSE NULL END) DNAME, 
	   ENAME, 
	   EMP_DEPTNO, 
	   SAL 
  FROM ( 
SELECT 'H' LEVELS,DEPTNO,DNAME,NULL ENAME,NULL EMP_DEPTNO,NULL SAL,DEPTNO REF_DEPTNO 
  FROM DEPT 
UNION ALL 
SELECT 'D' LEVELS, B.DEPTNO,B.DNAME,A.ENAME,A.DEPTNO,A.SAL,B.DEPTNO REF_DEPTNO 
  FROM EMP A, DEPT B 
 WHERE A.DEPTNO = B.DEPTNO 
) 
ORDER BY REF_DEPTNO,DECODE(LEVELS,'H',1,'D',2)

CREATE TABLE DEPT 
       (DEPTNO NUMBER(2) CONSTRAINT PK_DEPT PRIMARY KEY, 
	DNAME VARCHAR2(14) , 
	LOC VARCHAR2(13) ) 

CREATE TABLE EMP 
       (EMPNO NUMBER(4) CONSTRAINT PK_EMP PRIMARY KEY, 
	ENAME VARCHAR2(10), 
	JOB VARCHAR2(9), 
	MGR NUMBER(4), 
	HIREDATE DATE, 
	SAL NUMBER(7,2), 
	COMM NUMBER(7,2), 
	DEPTNO NUMBER(2) CONSTRAINT FK_DEPTNO REFERENCES DEPT)

INSERT INTO DEPT VALUES 
	(10,'ACCOUNTING','NEW YORK')

INSERT INTO DEPT VALUES (20,'RESEARCH','DALLAS')

INSERT INTO DEPT VALUES 
	(30,'SALES','CHICAGO')

INSERT INTO DEPT VALUES 
	(40,'OPERATIONS','BOSTON')

INSERT INTO EMP VALUES 
(7369,'SMITH','CLERK',7902,to_date('17-12-1980','dd-mm-yyyy'),800,NULL,20)

INSERT INTO EMP VALUES 
(7499,'ALLEN','SALESMAN',7698,to_date('20-2-1981','dd-mm-yyyy'),1600,300,30)

INSERT INTO EMP VALUES 
(7521,'WARD','SALESMAN',7698,to_date('22-2-1981','dd-mm-yyyy'),1250,500,30)

INSERT INTO EMP VALUES 
(7566,'JONES','MANAGER',7839,to_date('2-4-1981','dd-mm-yyyy'),2975,NULL,20)

INSERT INTO EMP VALUES 
(7654,'MARTIN','SALESMAN',7698,to_date('28-9-1981','dd-mm-yyyy'),1250,1400,30)

INSERT INTO EMP VALUES 
(7698,'BLAKE','MANAGER',7839,to_date('1-5-1981','dd-mm-yyyy'),2850,NULL,30)

INSERT INTO EMP VALUES 
(7782,'CLARK','MANAGER',7839,to_date('9-6-1981','dd-mm-yyyy'),2450,NULL,10)

INSERT INTO EMP VALUES 
(7788,'SCOTT','ANALYST',7566,to_date('13-JUL-87')-85,3000,NULL,20)

INSERT INTO EMP VALUES 
(7839,'KING','PRESIDENT',NULL,to_date('17-11-1981','dd-mm-yyyy'),5000,NULL,10)

INSERT INTO EMP VALUES 
(7844,'TURNER','SALESMAN',7698,to_date('8-9-1981','dd-mm-yyyy'),1500,0,30)

INSERT INTO EMP VALUES 
(7876,'ADAMS','CLERK',7788,to_date('13-JUL-87')-51,1100,NULL,20)

INSERT INTO EMP VALUES 
(7900,'JAMES','CLERK',7698,to_date('3-12-1981','dd-mm-yyyy'),950,NULL,30)

INSERT INTO EMP VALUES 
(7902,'FORD','ANALYST',7566,to_date('3-12-1981','dd-mm-yyyy'),3000,NULL,20)

INSERT INTO EMP VALUES 
(7934,'MILLER','CLERK',7782,to_date('23-1-1982','dd-mm-yyyy'),1300,NULL,10)

SELECT LEVELS , 
	   (CASE WHEN LEVELS = 'H' THEN DEPTNO ELSE NULL END) DEPTNO, 
	   (CASE WHEN LEVELS = 'H' THEN DNAME ELSE NULL END) DNAME, 
	   ENAME, 
	   EMP_DEPTNO, 
	   SAL 
  FROM ( 
SELECT 'H' LEVELS,DEPTNO,DNAME,NULL ENAME,NULL EMP_DEPTNO,NULL SAL,DEPTNO REF_DEPTNO 
  FROM DEPT 
UNION ALL 
SELECT 'D' LEVELS, B.DEPTNO,B.DNAME,A.ENAME,A.DEPTNO,A.SAL,B.DEPTNO REF_DEPTNO 
  FROM EMP A, DEPT B 
 WHERE A.DEPTNO = B.DEPTNO 
) 
ORDER BY REF_DEPTNO,DECODE(LEVELS,'H',1,'D',2)

SELECT LEVELS , 
	   (CASE WHEN LEVELS = 'H' THEN DEPTNO ELSE NULL END) DEPTNO, 
	   (CASE WHEN LEVELS = 'H' THEN DNAME ELSE NULL END) DNAME, 
	   ENAME, 
	   EMP_DEPTNO, 
	   SAL 
  FROM ( 
SELECT 'H' LEVELS,DEPTNO,DNAME,NULL ENAME,NULL EMP_DEPTNO,NULL SAL,DEPTNO REF_DEPTNO 
  FROM DEPT 
UNION ALL 
SELECT 'D' LEVELS, B.DEPTNO,B.DNAME,A.ENAME,A.DEPTNO,A.SAL,B.DEPTNO REF_DEPTNO 
  FROM EMP A, DEPT B 
 WHERE A.DEPTNO = B.DEPTNO 
) 
ORDER BY REF_DEPTNO,DECODE(LEVELS,'H',1,'D',2)