Postgres 17

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-- https://kb.databasedesignbook.com/posts/sql-joins/

create table A (a integer not null primary key);

create table B (b integer not null primary key);

create table C (c integer not null primary key);

insert into A values (1), (2);

insert into B values (2);

insert into C values (1), (2), (12);

CREATE TABLE

CREATE TABLE

CREATE TABLE

INSERT 0 2

INSERT 0 1

INSERT 0 3

select * from
  (select * from A left join B on a=b) AB left join C on b = c;

a
b
c

1
null
null

2
2
2

SELECT 2

select *
  from A left join (select * from B left join C on b=c) BC on a = b;

a
b
c

1
null
null

2
2
2

SELECT 2

a	b	c
1	null	null
2	2	2

a	b	c
1	null	null
2	2	2