If you want explicitly tell the query to some columns, you can specify the column names in SELECT clause. The following select statement returns only two columns from the table "departments":

SQL> SELECT location_id, department_name FROM DEPARTMENTS;

LOCATION_ID DEPARTMENT_NAME

----------- ------------------------------

  1700 Administration

  1800 Marketing

  1700 Purchasing

  2400 Human Resources

  1500 Shipping

  1400 IT

  2700 Public Relations

  2500 Sales

  1700 Executive

......