>I have a table called Enroll with fields stud_id and course_code.
>I want to set both of them as primary key.
>Is there any way yo do it? coz i don't know how to select 2 fields for the expression of the primary index. thanks

Assuming that they are both character data type, put 'course_code+stud_id' into the index key expression. If they are not, you'll have to convert them into the character type using STR(), PADL(), e.t.c.