Purpose of checking @@rowcount = 0 in a trigger?

Question

I've read a book For eg., Pro SQL Server 2008 Relation Database Design And Implementation Lois Davidson where I've found suggestion to check the @@rowcount inside the trigger: if it is = 0 then return:

if @@rowcount = 0 return

I'm wondering if the no row is modified how come trigger is fired?

Answer 1

The trigger fires for the statement being run. It will fire even if the table is empty, or if the statement affected no rows:

create table tr (i int);
go

create trigger g on tr after update
as 
print 'foo'
go


update tr set i = 2

@Muflix Update:

create table tr (i int);
go

create trigger g on tr after insert
as 
print 'foo'
go

insert into tr select * from tr;
go

As you see the trigger fires even if no rows were inserted.

Answer 2

Becuase Trigger won't be able to know how many rows are affected by the triggering event that is why you have to check inside.