Postgres 15

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select version();

version

PostgreSQL 15.18 (Debian 15.18-1.pgdg12+1) on x86_64-pc-linux-gnu, compiled by gcc (Debian 12.2.0-14+deb12u1) 12.2.0, 64-bit

SELECT 1

create table target (id int primary key, qty int);
insert into target values (1,10),(2,20);

create table source (id int, qty int);
insert into source values (2,5),(3,7);

CREATE TABLE

INSERT 0 2

CREATE TABLE

INSERT 0 2

-- MERGE arrived in PostgreSQL 15
merge into target t
using source s on t.id = s.id
when matched then update set qty = t.qty + s.qty
when not matched then insert (id,qty) values (s.id,s.qty);

MERGE 2

select * from target order by id;

id
qty

1
10

2
25

3
7

SELECT 3