The following query retrieves the personal details of all emp who ever taught an SQL course.
Correlated Subquery with EXISTS Operator
select e.* from emp e where exists (select o.* from offerings o where o.course = 'SQL' and o.trainer = e.empno);
You can also use an IN operator.
select e.* from emp e where e.empno in (select o.trainer from offerings o where o.course = 'SQL')
You can also use a join to solve the problem.
select DISTINCT e.* from emp e join offerings o on e.empno = o.trainer where o.course = 'SQL'
SQL> SQL> drop table emp; Table dropped.-- w w w.j a v a 2s . c o m 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> 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> SQL> drop table offerings; Table dropped. SQL> create table offerings( 2 course VARCHAR2(6) not null, 3 begindate DATE not null, 4 trainer NUMBER(4) , 5 location VARCHAR2(8)) ; SQL> SQL> insert into offerings values ('SQL',date '1999-04-12',7902,'DALLAS' ); SQL> insert into offerings values ('JSON',date '1999-08-10',7004,'CHICAGO'); SQL> insert into offerings values ('SQL',date '1999-10-04',7001,'SEATTLE'); SQL> insert into offerings values ('SQL',date '1999-12-13',7001,'DALLAS' ); SQL> insert into offerings values ('JAVA',date '1999-12-13',7004,'SEATTLE'); SQL> insert into offerings values ('XML',date '2000-02-03',7001,'DALLAS' ); SQL> insert into offerings values ('JAVA',date '2000-02-01',7011,'DALLAS' ); SQL> insert into offerings values ('PLS',date '2000-09-11',7008,'DALLAS' ); SQL> insert into offerings values ('XML',date '2000-09-18',NULL,'SEATTLE'); SQL> insert into offerings values ('JSON',date '2000-09-27',7902,'DALLAS' ); SQL> insert into offerings values ('ERM',date '2001-01-15',NULL, NULL ); SQL> insert into offerings values ('PRO',date '2001-02-19',NULL,'DALLAS' ); SQL> insert into offerings values ('RSD',date '2001-02-24',7008,'CHICAGO'); SQL> SQL> select e.* 2 from emp e 3 where exists (select o.* 4 from offerings o 5 where o.course = 'SQL' 6 and o.trainer = e.empno); EMPNO | ENAME | INIT | JOB | MGR | BDATE | MSAL --------- | -------- | ----- | -------- | --------- | ---------- | --------- COMM | DEPTNO --------- | --------- 07001.00 | SMITH | N | TRAINER | 07902.00 | 17-12-1975 | 01800.00 [N/A] | 00020.00 07902.00 | FORD | MG | 07004.00 | 13-02-1979 | 03000.00 [N/A] | 00020.00 SQL> SQL> SQL> select e.* 2 from emp e 3 where e.empno in (select o.trainer 4 from offerings o 5 where o.course = 'SQL') 6 SQL> SQL> select DISTINCT e.* 2 from emp e 3 join 4 offerings o 5 on e.empno = o.trainer 6 where o.course = 'SQL' 7