how to compare data from two tables

[divyanshu mishra]

hi ,
i am actually working on project where i have three tables A,B,C
i delete a table A completly and enter data in it every time the program runs.....
but in table B i just need to check that if corresponding isbn no not exists in table B then fetch them from table A and insert into table B.


can any one tell me how to write a mysql query for that.

** i am using isbn no as primary key.

thanks and regards:
divyanshu mishra