Show only new IDs and then update table so that next time query is run they won't show

Hi as the title suggest I would like to run a query that only shows New ID's.

Here is some test data 

create table #tmpmerchant (Com_id int not null)

insert #tmpmerchant values ('1234')
insert #tmpmerchant values ('23456')
insert #tmpmerchant values ('74895')
insert #tmpmerchant values ('9578')
insert #tmpmerchant values ('9579')
insert #tmpmerchant values ('444889')

So the first time this runs it will return all records.

I then want to store these IDs in a permanent table.

When the query is next run it will only show new IDs that are not in the permanent table.

insert #tmpmerchant values ('1234')
insert #tmpmerchant values ('23456')
insert #tmpmerchant values ('74895')
insert #tmpmerchant values ('9578')
insert #tmpmerchant values ('9579')
insert #tmpmerchant values ('444889')
insert #tmpmerchant values ('54789')

So in this example '54789' will only show.

The permanent table is then updated with the '54789'

What would be the best way to achieve this?

Regards