How to avoid multiple copies of data in page refresh

If you are talking about a page with an insert query, ignore the fact that it's a page refresh.  It's just another way that someone can insert duplicate records.  I like to handle this in my insert query.

insert into thetable

(f1, f2, etc)

select distinct

value1, value2, etc

from some_small_table

where you don't already have that record

Such as??