/* Qualifying a column to associate it to a table */

SELECT lname,  fname,  course_id
FROM   student, class
WHERE  student.ssn = class.stu_ssn;



/* You can qualify any column, not simply the joined columns */

SELECT student.lname,  student.fname,  class.course_id
FROM   student, class
WHERE  student.ssn  =  class.stu_ssn;