mysql - how do i improve cross join with 20,000 records? -

i have 2 tables: users (userid,student_no,name) , regd (semester,student_no). users contain 7,000 records , regd contains 20,000 records. there entries in regd not in users.

how quickly select entries in users have entries in regd semester = '2012-2'? tried this:

 select *  `regd` , users       semester =  '2012-2' , users.student_no = regd.student_no 

but taking forever load queries if have tiny database. every 6 months, 10,000 entries added regd , 2,500 entries added users each year.

add indexes on join columns:

create index idx_regd_student_no on regd(student_no); 

and

create index idx_users_student_no on users(student_no); 

also, if tables don't have pk, add one. in case of regd, can use pk = (semester, student_no).

as other comments say, 22k records not big, can assume without decent index.

hope helps.