scenario for insert query
i've two tables tab1 and tab2 both tables have four columns. reg_no, page_no, comments. reg_no and page_no having composite key. now i want to write query which insert the records in tab2 by selecting from tab1 and only insert those records which r not in tab2. like in tab1 there two records reg_no=1 and page_no=1, reg_no=1 and page_no=2 while tab2 there are also two records reg_no=1 and page_no=1, reg_no=2 page_no=1 now i want that i write an insert query which check duplicate records and only insert reg_no=1 and page_no=2 otherwise it shows primary key voilation. can any1 help me about this query.