Postgres 18

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select version();

version

PostgreSQL 18.6 (Debian 18.6-1.pgdg12+2) on x86_64-pc-linux-gnu, compiled by gcc (Debian 12.2.0-14+deb12u1) 12.2.0, 64-bit

SELECT 1

create table x
(
  v int
);

insert into x values (1), (null);

CREATE TABLE

INSERT 0 2

create table y
(
  v int
);

insert into y values (1), (null);

CREATE TABLE

INSERT 0 2

select x.v, y.v 
  from x
  join y
    on exists (select x.v
               intersect
               select y.v)

v
v

1
1

null
null

SELECT 2

v	v
1	1
null	null