in postgree, assume I have a tmp table, which is the following schema

tmp_data

id   |  name   | ...
--------------------
null | 'test'  | ...
10   | 'other' | ...

and I have initial table data which has the same schema

id   |  name   | ...
--------------------
1    | '1'     | ...
2    | '2'     | ...

I want to upsert from initial tmp table into final table, and return all ids, so I was thinking to write this query

insert into data (id, name, ...)
select id, name
from tmp_data
on conflict update
set name = excluded.name
returning id

but the problem is that id is auto generated, so – I want to insert the value if it exists (10) and generate if not (null)

I tried to use select case if column null than default – but seems default cant be used in select clause

Splitting query into 2 is not a case for me, as I am using that data in ef core, and I need to do this in 1 batch – and get ids

Result I am expecting

id   |  name   | ...
--------------------
1    | '1'     | ...
2    | '2'     | ...
3    | 'test'  | ...
10   | 'other' | ...

Are there any options?