Postgres 10

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create table test1 (id int primary key, col int);
create table test2 (id int, col int);
insert into test2 values (1,1), (2,2)
2 rows affected

insert into test1 values (1,0)
1 rows affected

insert into test1 (id, col)
select * from test2
where col < 9
ERROR:  duplicate key value violates unique constraint "test1_pkey"
DETAIL:  Key (id)=(1) already exists.


select * from test1


id
col


1
0


insert into test1 (id, col)
select * 
from test2 
where col < 9
on conflict (id) do
update set col = excluded.col
2 rows affected

select * from test1


id
col


1
1

2
2