drop table t1;
drop table t2;
drop table t_changes;

create table t1
(id INT,name text, new_id INT default(0));

create table t_changes
(old_id INT,new_id int)

insert into t1(id,NAME)
VALUES (1,'n1'),(2,'n2'),(3,'n3');

insert into t_changes(old_id,new_id)
values(1,11),(2,12),(3,13),(4,13)

select * from t1;
select * from t_changes;

-------!!!!
update t1
set new_id = n.new_id
from t1 t 
inner join t_changes n
on n.old_id=t.id;

select * from t1
------------------------------
"id"	"name"	"new_id"
-----------------
"1"	"n1"	"11"
"2"	"n2"	"11"
"3"	"n3"	"11"