One of my frieds told me that INSERT trigger will not fire if no data are added to the main table. It is a mistake that some people think that triggers will not fire if no row is affected. Note that trigger is event based and not data based.
Here is a proof that trigger fires eventhough no row is affected.
Consider this table
create table testing(prod_id int , prod_name varchar(100))
and create this trigger
create trigger test_trigger on testing
raiserror ('The insert trigger is fired',10,16)
Now execute the following code that adds no row to the table
insert into testing(prod_id ,prod_name )
select 1,'test' where 1=0
The message retuned is
The insert trigger is fired
(0 row(s) affected)
So it is clear that when a statement is valid, trigger will fire no matter how many rows are actually affected