Postgres 14

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create table a (
   id int not null primary key
 , val text
);

insert into a
select n, 'A-' || n::text
  from generate_series(1,4) n;
  
select *
  from a;
4 rows affected



id
val


1
A-1

2
A-2

3
A-3

4
A-4


create table b (
   id int not null primary key
 , val text
);

insert into b
select n, 'B-' || n::text
  from generate_series(3,7) n;
  
select *
  from b;
5 rows affected



id
val


3
B-3

4
B-4

5
B-5

6
B-6

7
B-7


insert into a
select *
  from b
ON CONFLICT DO NOTHING;

select *
  from a;
3 rows affected



id
val


1
A-1

2
A-2

3
A-3

4
A-4

5
B-5

6
B-6

7
B-7