continuous copy/update one table to another

Hello,

I am looking for a way to copy all the data from one table to another
on a regular basis, every 5 minutes let's say.

INSERT INTO table2 SELECT * FROM table1;

The above will copy all the data as is and insert it into the other
table.  What happens if I rerun it again?  Will it just append table1
again into table2?  How can I have it only insert rows that are
different?  Would that be a program to lookup the most last record in
table 1 and then a query to only select after that row for the insert
into table2?

Thanks!