Oracle SQL - Write SQL to get which courses have been held in Chicago and/or in Seattle?

Requirements

Here is the table

Demo

SQL>
SQL> drop table offerings;

Table dropped.-- www .  j  a v  a 2 s  .c om

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>

Write SQL to get which courses have been held in Chicago and/or in Seattle?

Demo

SQL>
SQL> select distinct course
  2  from   offerings
  3  where  location in ('CHICAGO','SEATTLE');

COURSE-- from   ww  w.  ja  v  a2 s  . c om
------
JAVA
XML
SQL
JSON
RSD

SQL>