How to do an upsert when updating a table from another table postgres?

Question

I have table A that contains about 10 millions rows and Table B which contains some updated information for some rows in table A and also contains new rows that don't exist in table A .

I want to update table A using table B and at the same time insert rows that have no match in table A .

I found many answers like the solution below but it seems like they all miss the inserting part that I'm looking for.

UPDATE A 
SET code = B.code
FROM B
WHERE A.id = B.id 

Answer 1

Use two queries:

update a
    set code = b.code
    from b
    where a.id = b.id;

insert into a (id, code)
    select id, code
    from b
    where not exists (select 1 from a where a.id = b.id);

You can also use on conflict

insert into a (id, code)
    select b.id, b.code
    on conflict on constraint a_id
    do update set code = b.code;