Here is the table
SQL> SQL> drop table emp; SQL> create table emp( 2 empno NUMBER(4) primary key, 3 ename VARCHAR2(8) not null , 4 init VARCHAR2(5) not null , 5 job VARCHAR2(8) , 6 mgr NUMBER(4) , 7 bdate DATE not null , 8 msal NUMBER(6,2) not null , 9 comm NUMBER(6,2) , 10 deptno NUMBER(2) default 10) ; SQL>-- w ww . j av a2s . c om SQL> insert into emp values(7001,'SMITH','N', 'TRAINER', 7902,date '1975-12-17', 1800 , NULL, 20); SQL> insert into emp values(7002,'ALLEN','JAM','SALESREP',7006,date '1971-05-20', 1600, 300, 30); SQL> insert into emp values(7003,'WARD', 'TF' ,'SALESREP',7006,date '1972-03-02', 1250, 500, 10); SQL> insert into emp values(7004,'JACK', 'JM', 'MANAGER', 7009,date '1977-04-02', 2975, NULL, 20); SQL> insert into emp values(7005,'BROWN','P', 'SALESREP',7006,date '1976-09-28', 1250, 1400, 30); SQL> insert into emp values(7006,'BLAKE','R', 'MANAGER', 7009,date '1973-11-01', 2850, NULL, 10); SQL> insert into emp values(7007,'CLARK','AB', 'MANAGER', 7009,date '1975-06-09', 2450, NULL, 10); SQL> insert into emp values(7008,'SCOTT','DEF','TRAINER', 7004,date '1979-11-26', 3000, NULL, 20); SQL> insert into emp values(7009,'KING', 'CC', 'DIRECTOR',NULL,date '1972-10-17', 5000, NULL, 10); SQL> insert into emp values(7010,'BREAD','JJ', 'SALESREP',7006,date '1978-09-28', 1500, 0, 30); SQL> insert into emp values(7011,'ADAMS','AA', 'TRAINER', 7008,date '1976-12-30', 1100, NULL, 20); SQL> insert into emp values(7012,'JONES','R', 'ADMIN', 7006,date '1979-10-03', 8000, NULL, 30); SQL> insert into emp values(7902,'FORD', 'MG', 'TRAINER', 7004,date '1979-02-13', 3000, NULL, 20); SQL> insert into emp values(7934,'MARY', 'ABC','ADMIN', 7007,date '1972-01-23', 1300, NULL, 10); SQL>
Write SQL to list emp who don't have subordinates
SQL> SQL> select empno, ename, init 2 from emp-- w w w . j av a 2s.c o m 3 where empno not in (select mgr 4 from emp 5 where mgr is not null); EMPNO ENAME INIT ---------- -------- ----- 7005 BROWN P 7011 ADAMS AA 7010 BREAD JJ 7003 WARD TF 7012 JONES R 7934 MARY ABC 7002 ALLEN JAM 7001 SMITH N 8 rows selected. SQL>